Physics Form Four Study Notes

TOPIC: 1

WAVES

A wave: Is a periodic mechanism which transfers energy from one form to another of energy. Or

Is a disturbance that travels through a medium from one location to another location

A pulse: Is a single disturbance moving through a medium from one location to another location.

Practically: Wave: Is the progressive disturbance propagated from a point in a medium on space without the movement of the medium

A medium: Is a substance or material that carries the wave from the source to other location

For example: the news media refers to the various institutions (newspaper offices, television stations, radio stations, etc.) within our society that carry the news from one location to another. The news moves through the media.

Qn: Is the wave medium also the waves explain:

Answer The wave medium is not the wave and it doesn't make the wave; it only carries or transports the wave from its source to other locations.

Examples of waves: Water waves, Light waves, Radio waves, Sound waves

Terms associated with waves

Consider the graph of displacement against time

1. The amplitude (A) Is the maximum displacement of the wave particles from their rest position to crest or trough.

Hence it is measured from the rest to the crest or to the trough position in metres

2. The crest: Is the point of the maximum amount of positive or upward displacement from the rest position

3. The trough: Is the point of the maximum amount of negative or downward displacement from the rest position

4. Period (T) Is the time taken for a wave to complete one cycle

The SI Unity of period is seconds

5. Frequency (f) Is the number of complete cycles (oscillation) per second. Or

Is the number of crests or troughs that pass a given point per unity time

The SI unity of Frequency is Hertz (Hz); 1Hz = 1S^-1

The relationship between frequency and periodic time is that: f = , T =

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Consider the graph of displacement against distance below

6. The wavelength (λ) Is the distance between two adjacent crest or trough. Or

Is the length (distance) that the wave travel to complete one cycle

From the graph the wave length is 20 Metres

7. Wave velocity (V) Is the distance travelled by a wave per unity time. Or

Is a speed by which a wave passes through a medium

The relationship between f, V, and λ

From the definition of terms above, therefore: , f = , T =

Therefore V = λ ÷ or V = λ x f,

V = f λ , λ = , f =

Example: 1. The distance for a wave to complete one cycle is 46M and their wave speed is 340m/s. Calculate (i) Wavelength (ii) Frequency (iii) the periodic time

Data Information:

(i) Wave length = Distance to complete one cycle = 46M

(ii) f = =

(iii) From T = =

Types of Waves according to the media of propagation

1. Electromagnetic Waves

2. Mechanical Waves

1. Electromagnetic waves (EMW)

Is the type of waves that does not requires materials medium to propagate (to transfer energy or (through which it passes)

Note: It transfers energy from one place to another through an empty space (Vacuum

or air). Examples of this wave are Radio waves (signals), Visible light

2. Mechanical Waves (Elastic wave) MW

Is the type of waves that requires materials medium for transmission of energy Examples: Water waves, Sound waves, Waves in a helical spring, Earth quake waves

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Types Mechanical

1. Transverse waves

2. Longitudinal waves

3. Surface waves.

1. Transverse waves

In transverse waves, the medium (water) moves perpendicular to the wave direction

Eg. Water waves: Water particle moves up and down while the water wave’s move in horizontal direction hence makes perpendicular movement or transverse

2. Longitudinal waves

Is the wave in which the particles vibrate parallel to the wave direction

Longitudinal waves produce two pattern called compression and rarefaction

In compression the wave particles are parked closely together while in Rarefaction the particles are spread out in the direction of waves

3. In surface waves, both transverse and longitudinal waves mix in a single medium In very simple words, an electronic wave is that which travels in a vacuum, and a mechanical wave is that which needs some medium for travelling

Examples of mechanical waves are Sound waves, Water waves , Ocean waves, Earth quake waves, Seismic waves

The following are the differences between mechanical and electromagnetic waves

• Electromagnetic waves travel in a vacuum whereas mechanical waves do not.

• The mechanical waves need a medium like water, air, or anything for it to travel.

• While an electromagnetic wave is called just a disturbance, a mechanical wave is considered a periodic disturbance.

Behaviour of Waves

All waves behave in certain characteristic ways. They can undergo:

a) Reflection

b) Refraction

c) Diffraction

d) Interference

a) Reflection

Is the change in direction of a wave front when hit or encounter a boundary that cannot pass therefore returns into the medium from which it originated

How it occurs is that: when the boundary is fixed (cannot move) the wave can reflect in inverted way but if the boundary is free to move the wave reflects in erect way (upright) and will move in the same speed and wavelength as the incident wave but with smaller amplitude because some energy is lost at the boundary

If the reflecting surface is very smooth, the reflection of light that occurs is called specula or regular reflection. The laws of reflection are as follows:

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The 1^st law states that “The incident ray, the reflected ray and the normal to the reflection surface at the point of the incidence lie in the same plane”

The 2^nd law states that “The angle which the incident ray makes with the normal is equal to the angle which the reflected ray makes to the same normal”

The 3^rd law states that “The reflected ray and the incident ray are on the opposite sides of the normal”

Ripple Tank

A ripple tank Is a shallow glass tank of water used to demonstrate the basic properties of waves

Fig. Ripple tank

How ripple tank works

Parts of the ripple tank

1. Shallow tank of water in a glass basin in which an oscillating paddle generates parallel water waves

2. A lamp (illuminator) that shine light though the water

3. Sheet of paper placed under the tank in which a shadow of the wave pattern is produced

4. The stroboscope

A stroboscope (strobe)

Is an instrument used to make a cyclically moving object appear to be slow-moving or stationary

Functions (Role) of stroboscope in a ripple tank

1. Is used to measure frequencies of rotating objects

2. It makes moving objects speed to appear slow-moving

3. It is used to adjust the frequency of the flash by seeing it appear stationery or moving slowly backward of forward depending on the flash frequency

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Application of reflection of light

1. It is used in the design of mirrors in which light waves bounce on striking slivery surface

2. It is used to measure distance of waves eg. Sound waves

3. Sonar (sound navigation and ranging) system assists ships in navigation, communication and detecting other vessels

b) Refraction of waves

Is the change in direction and speed of propagation of a wave due to a change in its transmission medium.

When water waves travel from a shallow part to a deep part its wavelength decrease while frequency is constant hence the velocity of the wave decrease

Snell‘s law

Refraction is described by Snell's law, which states that:

For a given pair of media and a wave with a single frequency, the ratio of the sines of the angle of incidence θ1 and angle of refraction θ2 is equivalent to the ratio of phase velocities (v1 / v2) in the two media, or equivalently, to the opposite ratio of the indices of refraction (n2 / n1)

From Snell’s law

Application of refraction of waves

1. It is used to determine the shininess of the objects: the more shines the more

2. It is used to spread light in optical instruments. Microscope and telescope

3. It is used to determine the eye’s refractive error in hospital

c) Interference

Is the condition in which two waves of the same amplitude are travelling in the same frequency and producing a new wave pattern after interaction

This happens because they come from the same source or because they have the same or nearly the same frequency.

Principle of superposition of waves

This states that: The resultant displacement of the wave at any point is equal to the sum of the displacement of different waves at the point

This means that: If the crest of one waves meets the crest of the other waves in the same direction the amplitude formed will be increased. Hence this is referred to as constructive interference

Types of interference

Constructive interference and destructive interference

1. Constructive Interference

Is a type of interference that occurs at any location along the medium where the two interfering waves have a displacement in the same direction

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2. Destructive Interference

Is a type of interference that occurs at any location along the medium where the two interfering waves have a displacement in the opposite direction.

Eg. When a crest meets a trough: the resulting waves have smaller amplitude

Application of interference of waves

1. It is applied in the construction of hologram

Hologram: Is a photograph of interference pattern which is able to produce a three dimensional image when suitably illustrate

2. It is used in noise reduction system. Eg Earphones

d) Diffraction of waves

Is a change in direction of waves as they pass through an opening (gap) or around a barrier in their path.

During diffraction he following re observed

1. The apparent bending of waves around small openings (gap)

2. The spreading out of waves when they pass through gap

Qn: Explain how does the size of gap in a barrier affects the diffraction of waves

Answer: The spreading out of waves depends on size of the gap as fallows and the wavelength:- That

· The bigger the gap the wave emerge almost straight in all direction

Fig. Wave spreading in wider gap

· When the gap is narrow the wave appear to circular and spread out round in all direction

Fig. Wave spreading in a narrow gap

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Application of diffraction of waves

1. it is used to determine the crystal structure of materials

2. it is used to take measurements in

· Crystallite size, Thickness of thin films, Coefficient of thermal expansion

Sound Waves

This is the wave produced by vibrating objects. Such as turning fork

The sound waves require material medium for propagation

Note. The sound reach another objects when the first object vibrate and particles transfers energy to other objects

Note: If particles are closer together sounds travels faster. Eg in sold than in liquids

Sources of sound waves

The source of sound it is where the sound starts (produced)

It may be People, Animals, Machines

Musical instruments are designed to produce specific sound. This musical instrument includes Guitar, Violins, Pianos, Organs, Recorders, Flutes, Drums, Marimbas

The Concept of Audibility

Audibility range: Is the range of frequencies that can be detected (heard) by ears

The average human ear can detect sound in the frequency range of 20 to 20,000Hz,

But the ear is most sensitive to sound with a frequency round 3,000Hz

Infrasonic and ultra sonic sounds

Infrasonic sound: Is the sound with frequency below 20Hz

Ultrasonic sound: Is the sound with frequency above 20,000Hz. Animals including Dogs, Bats, Cats, Dolphins fall in the ultrasonic sounds

Note: the average human ear can distinguish between two sounds if their frequencies differ by at least 7Hz

The Concept of Echo and Reverberation

An echo (Sound in Greek): Is the reflected sound which is heard distinctly from the original sound

Occurrence of Echo: This occurs when a reflected sound reaches the ear more than 0.1sconds after the original sound was heard

This is because at this time interval the sensation of the original sounds will have died out and the reflected sound will be heard

Note: The echo is produced due to hitting of the sound waves with the obstacles which makes the sound to reflect back

Note: For a sound to be reflected (heard) it must travel to the obstacle and then return the same distance to the source of sound. The minimum time that the sound should reach the obstacle is = 0.05seconds

The speed of sound in air at 25˚C is 340m/s

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Therefore the distance the waves travel from the source to the obstacle is

From , Distance = Speed x Time

Distance = 340 x 0.05 = 17M

For an echo to be heard (occurs) an obstacle must be at least 17M away from the source of sound. Therefore from the source (listener) to the obstacle the sound travels a distance equal to 2d. Hence to calculate the speed of echo use

Example: 2. If the distance from the source to the wall is 480m and the time taken for a wave to move from the source to the wall is 6seconds. Calculate the speed of the wave

Data information

Distance = 480m, time = 6seconds, speed = ?

From

Example: 3. The distance from the source to the obstacle is 430m and the time taken for a sound to be heard is 2.5seconds. What is the speed of the wave

Data information

Distance = 430m, time = 2.5m, velocity = ?

From

The speed of wave in dry air is calculated practically by

Velocity (V) = (331.4 + 0.6Tc)m/s

Where Tc = The temperature at which the speed is measured

Note: The speed of sound in air increase with temperature that; as the temperature increases the speed of sound also increases. Sound travel faster in solids than in liquids and air

Example: 4. A loud sound is made and the echo from a cliff is heard 8seconds later. If the atmospheric temperature is 22˚C. How far away is the cliff

Data information

Time = 8seconds, V = (331.4 + 0.6x22) = 344.6m/s

From

Reverberation

Reverberation: Is the multiple (collection) reflection of sound in an enclosed space (cavity)

A reverberation is the same as echo but the distance in reverberation between the source of the sound and the obstacle by which it is reflected is less and the time is less

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than 0.1seconds, also reverberation is due to collection of reflected sound waves from the surface which is enclosed completely while echoes is due to reflection of sound waves by obstacle (wall)

The Concept of a Musical Sound

Music: Is organised sound which has some pattern

Music uses certain frequencies or combinations of frequencies called the musical scale to produce sounds that are heard to the human ear

Noise: Is a random sound and without structure

Properties of musical sounds

The musical sounds produced by different musical instruments have distinct properties that are used to describe them. These include loudness, pitch and timbre

· Loudness: Is the intensity of the sound which is the perceptual property (as perceived by human ear)

It is determined by the amplitude of sound wave that; the larger the amplitude the louder the sound.

• Pitch: Is the property of sound according to which sounds can be ordered on a scale from high to low. Or Is the property of the note that is used to differentiate a high note from a low note

The pitch is determined by the frequency of waves that; the higher the frequency the higher the pitch of the sound wave produced and vice verse. The pitch is higher when the tight string is plunked and low when the loose string is plunked

• Quality/Timbre: Is the sound quality/colour produced by an instrument.

This is what makes a particular musical sound different from another, even when they have the same pitch and loudness

Different Musical Instruments

Musical instruments: Are the device constructed or modified for the purpose of making/producing music. They are categorized (are based) on according to the initially produces the sound these includes Wind instrument, string instruments and percussion instruments

1. Wind Instruments: They are made by a tube in which a column of air is set into vibration by the player blowing into a mouthpiece at the end of the tube; they include Recorders, Flutes and Trumpets

2. String instruments: They produce sound from stretched strings that are plunked, bowed and or struck. Plunked eg guitar, Bowed eg. violin and Struck eg. piano

3. Percussion instruments: They produce musical sounds by being struck with any action that set them into vibration. Eg shaken, scrapped etc. They include Drum, Cymbals and Marimba

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Fundamental Note, Harmonics and Overtones

Fundamental frequency (Fo): Is the lowest frequency produced by a vibrating string or pipe

Fundamental note: Is the corresponding note produced by a fundamental frequency lowest resonant frequency of a vibrating object

Note: Fundamental frequency (note) = 1^st Harmonic (H₁)

An Overtone: Is any frequency higher than the fundamental frequency of a sound produced by fundamental notes

For a string of length L. fixed at both ends, the wavelength of the n^th harmonic (λ_n) is given by , where n = number of harmonic

Since V = ʎf then the frequency (fn) of the n^th harmonic is calculated by

From f =

Therefore Fondamenta frequency (note) (Fo) First harmonic (F_o or H₁)

Fo = H₁

Stationary Waves in Strings

A stationary wave: Is a wave in a medium in which each point on the axis of the wave has associated constant amplitude

If a stretched string is fixed at both ends plunked and release then a stationary wave is formed by the superposition of incident and reflected waves

Odd Harmonics n = 1, 3, 5...

Consider the string below fixed at two ends and plunked at the middle

ʎ = 2l, but V = f ʎ, f = V/ʎ

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If the string is plunked harder at the middle it will be

If F = First overtone

This is the second harmonic (H₂) = 3Fo = First Overtone

H₂ = 3Fo = First overtone

Harmonic: Is the note with a frequency equal to multiple of the fundamental frequency

Is a whole number multiple of a fundamental frequency

If the string is plunked harder at the middle it will be

H₃ = 5Fo = Second overtone

General formula (equation) for a odd harmonic when given Fo is

Fn = (2n + 1) Fo

Nodes: The locations at which the amplitude is minimum

Antinodes: The locations where the amplitude is maximum

Even Harmonic n = 2, 4, 6...

They are produced when a string is plunked in ¼ or 1/8 of its length

For the first harmonic the string is plunked at the middle (centre)

Before plunked After plunked

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From F1 =

This is the second harmonic (H2) = 2Fo = First overtone

When plunked harder and produce four cycles

This is the H3 = 4Fo = Second overtone

General formula for Even harmonic is

Fn = 2nFo n = Number of overtones

Factors affecting the f of vibrating wire

The frequency produced by vibrating string depends on

Length of the string and the velocity of the wave

But the velocity of waves on a stretched string depends on the tension (T) and the linear mass density ( )

The linear mass density ( ): Is the mass of the string per unit length

the SI Unity is Kg/m

The frequency of vibrating wire (a music note) depends on the length, mass per unit length and the tension

Their relationship is that

Constant

F₁l₁ = f2l₂

Constant

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By combining equations (i), (ii) and (iii) as i x ii x iii

Where T = Tension, L = Length, μ = Linear mass density, ½ is const from experiment

Example: 5. A string has a length of 75cm and a mass of 8.2kg. if the spring has a tension of 18N. What are the frequency of the first and second harmonic

Data information

L = 0.75m, M = 8.2kg, T = 18N

From =

(i) From

Fo = F1 =

Frequency of the first harmonic is (Fo) = 27Hz

(ii) Third harmonic (H3) = F3 = 3Fo

H3 = 3 x 27 = 81Hz

Frequency of the third harmonic is (3Fo) = 81Hz

Forced vibrations

Are vibrations that occurs in a system as a result of impulse received from another system vibrating nearby

Resonance

Is a large pronounced loud sound obtained when forced vibration and natural vibration both reach the same frequency

Qn: Explain how resonance occurs: Resonance occurs in sound when forced vibrations and natural vibrations both reach the same frequency and large pronounced sound is obtained

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Vibration of air in pipes

There are two types of pipes that include (i) Closed pipe (ii) Open pipes

(i) Closed pipe

Is a pipe which is closed at only one end point

For the second harmonic (H2) First overtone

From fig. ,

General formula Fn = (2n+1)Fo n = Number of harmonic

Where n = 0, 1, 2, 3...

N = 0 H1

Fo = (2 x 0 + 1) F0 = 1F, Fo = 1Fo, Fo = Fo

Where n = 1, H₂ First overtone

F₁ = (2 x 1 + 1)Fo = 3Fo

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Example: 6. A turning fork of frequency 512Hz is sounded at the mouth of a tube closed at one end with a column of air with 18.0cm long again when a column of air is 51cm log. Determine the velocity of sound in air

Data information

f = 512Hz, L1 = 0.18m, L2 = 0.51m

From

L2 - L1 =

Then V = f ʎ = 512 x 0.66 = 338m/s

Therefore velocity of sound in air = 338m/s

Example: 7. In a closed pipe the first resonance is at 23cm and second at 73cm. Determine the wavelength of the sound and the end correction of the pipe

Data information

L1 = 0.23m, L2 = 0.73m, ʎ = ?, C = ?

(a) From

L2 + C - L1 + C =

Wavelength = 1M

End correction is at 0.02M

(ii) Open pipes (Even Harmonic)

Here both ends of the pipe are open

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In this pipe there is two end corrections

Example: 8. A turning fork of frequency 250Hz is used to produce resonance in open pipes. Given that the velocity of sound in air is 350m/s. Find the length of the tube which gives (a) The first resonance (b) The third resonance

Data information

f = 250Hz, V = 340m/s

From

(a) From

Length of the first resonance = 0.7m

(b) From

Length of the third resonance = 2.1m

Consider the following relation for derivation of formula

L2 - L1 =

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L2 - L1

But V = f ʎ

Example: 9. In a certain resonance tube experiment the short length of 0.44m and the next length of 0.96m are used together. Calculate the frequency of vibration. If the velocity is 340m/s

Data information

L1 = 0.44m, L2 = 0.96m, V = 340m/s, f = ?

Frequency of vibration = 327Hz

Beat: Is a rise and fall in loudness of sound when two sources of sound of nearly equal

frequencies produce sound together

Beat frequency = differences in frequencies

Bf = F1 - F2 used if F1 > F2 or

Bf = F2 - F1 used if F2 > F1

Example: 10. A 268Hz turning fork produces sound with 300Hz for fork at same time. Calculate the beat frequency

Data given

F1 = 268Hz, F2 = 300Hz, Bf = ?

From Bf = F2 - F1

= 300Hz - 268Hz = 32Hz

Beat frequency Bf = 32Hz

Example: 11. The frequency of the turning fork of 444Hz is at 150cm. Calculate the frequency for the length of 200Hz

From L1f1 = L2f2

Frequency of the second length is 333Hz

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The Concept of Electro-magnetic Spectrum

The electromagnetic spectrum: Is the range of frequencies of electromagnetic radiation

Is a continuous band of all electromagnetic waves arranged in order of increasing or decreasing frequency or wavelength

The electromagnetic waves on the other hand propagate in air thereby does not require material medium for them to propagate

Note: Electromagnetic waves are produced when electrically charged particles oscillate or change energy. The greater the energy changes the higher the frequency of the respective wave. Therefore in vacuum electromagnetic waves propagate at a speed of light

The electromagnetic spectrum extends from the low frequencies used for modern radio communication to gamma radiation at the short-wavelength (high-frequency)

Arrangements of principle regions of the electromagnetic waves by the increase in frequencies and the decreases (short) in wavelength hence they includes

1. Radio waves 2. Microwaves 3. Infrared radiation 4. Visible light 5. Ultraviolet

(UV) rays 6. X-rays 7. Gamma rays

Properties of electromagnetic wave (spectrum)

1. They do not require material medium to propagate

2. They undergo the properties of waves such as reflection, diffraction, interference, refraction because they are waves

3. They travel with the speed of light i.e. 3x10⁸m/s (all EMW travel with this speed

4. They carry no electric charges

5. They obey the wave equation C = f ʎ

6. They transfer energy from a source to a receiver in form of oscillating electric and magnetic field

Note: These radiations in some cases there is an overlap in the range of wavelengths because sometimes the name given to this radiations is determined from the sources and not wavelength or frequency. Eg. x – rays and gamma rays

1. Radio waves : This have the longest wavelength and short frequency in EMS

This wave can be divided into long wave (LW), medium waves (MW) and short waves (SW); the short waves include very high frequency (VHF) and ultra high frequency (UHF) waves

Sources of radio waves

(i) Alternating electric current flowing in special conductors called antenna

(ii) Special circuit called oscillators

(iii) Objects in space such as planets, comets, stars and galaxies

Detection of radio waves

Are detected using specially designed antenna such as those used in radios and television (TV)

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Uses of radio waves

(i) Are used in broadcasting of information by radios and television channels

(ii) Are use by astronomers to collect and study radio waves from distant stars and galaxies by helping them to determine composition, structure and motion of the celestial bodies

2. Microwaves: Have a short wavelength of between 10^-4m to about 0.1m

Source of microwaves

(i) Are produced by oscillation of charges in special antennae mounted on dishes

(ii) Are produced in devices called magnetron

Detection of microwaves

Are detected using special receivers which convert radio wave energy to sound

RADAR = Radio detection and ranging: Is a technology which uses radio waves to detect and determine the position of objects

Use of microwaves

(i) Are used in cooking in a microwave oven

(ii) Rader systems use microwaves to detect the position, speed etc. of remote objects

(iii) Are used in long-distance communication because they are not affected by clouds or other atmospheric conditions

3. Infrared waves (radiations): Have a frequency of between 10¹² to 10¹⁴ Hz

They are close to the microwaves because of the heating effects they have

Sources of infrared radiation

(i) It is produced by vibration of atoms and molecules due to thermal energy

(ii) From all hot bodies

Detection of infrared radiation

(i) By touching or holding near hot objects you feel it

(ii) Can be sensed far from visible light as heat

Can be detected using devices such as black bulb thermometers, photographic films, thermistors and photo-transistors

Uses of infrared radiation

(i) In cooking food in conventional ovens

(ii) Are used in remote controls, night-vision devices, security system, fibre-optics communication

(iii) Are used in taking image of an objects in the temperature range 250˚C and 500˚C

4. Visible light: Is the narrow range of electromagnetic wave to which frequency of human eye are sensitive

Source of visible light

Is produced by electron transitions within an atom. 50% of radiation emitted by the sun is visible light

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Detection of visible light

It is detected using eyes, photographic films and photocells

Uses of visible light

1. It is used by vision using eyes

2. It is in taking photography

3. It is used in photosynthesis in plants

Note: We see things because they either emit visible light or because they reflect visible light from another source.

5. Ultraviolet (UV) light:

Source of UV light

(i) Is produced by electron transitions within an atom but more energetic

(ii) It is emitted by very hot objects. Eg the sun

(iii) Electric arcs used for welding

Detection of UV light

By using photographic films fitted with quartz glass lenses and not ordinary glass

By using fluorescent materials which absorb UV light and re-emit it as visible light

Uses of UV light

(i) Stimulate the production of vitamin D in human skin

(ii) Treatment of skin conditions such as psoriasis

(iii) Used as germicidal agent in the sterilisation of food and purification of air and water

(iv) Use in banks to detect forged documents and fake currencies

6. X- rays: Are EMW with short wavelength and very high frequency.

They are called ionising radiation because can cause atoms and molecules with which interacts to loos one or more electrons. Thus producing ions

Sources of X- rays

Are produced when electrons that have been accelerated to very high velocities hit a metal target in an X-ray tube

Detection of X-rays

(i) Using photographic plate; which it affects them

(ii) Using an X-ray film in a cassette:-

(iii) Using rare earth element screens:-

Uses of X-rays

(i) Are used in diagnosis and treatment of cancer

(ii) Taking x-rays photography and display shadow

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7. Gamma rays: Are the most energetic of the EMW like X-rays also cause ionisation in matter

Sources of gamma rays

(i) Are produced in space by things such as solar flashes, supernovae, neutron stars, black holes and active galaxies

(ii) Are produced by radioactive decay of atoms (natural radioactivity or nuclear fission

Detection of gamma rays

Can be detected using photographic films, Geiger-Muller tube and Cloud chamber

Uses of gamma rays

Have the same application as X-rays which include

In agriculture to obtain new plant varieties which are diseases resistant and give more yields

REVIEW QUESTIONS ON CHAPTER - 1

1. (a) (i) Define wave

(ii) Mention two categories of waves and explain them

(b) Give at least four examples of waves you mentioned in (a) (ii) above

2. (a) Define the following parameters and give their SI Unity

(i) Amplitude (ii) Periodic time (iii) Frequency (iv) Wavelength

(v) Velocit of a wave

(b) (i) The figure below shows the displacement of a wave with time

Determine the following Amplitude, Periodic time and Frequency

(ii) The figure below shows the graph of displacement against distance

both in metres also by referring graph in (b) (i) above. Determine

wavelength and the velocity of the wave

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3. (a) (i) State the relationship between Frequency and Tension

(ii) Velocity, Frequency and Wavelength

(b) The distance from the equilibrium position to a point is 25m and heir

wave speed is 350m/s/ calculate (i) Frequency (ii) periodic time

4. (a) Explain the wave behaviour

(b) State the necessary conditions for constructive and destructive

interference to occurs in two waves

(d) Under what conditions the echo and reverberation are said to occurs

5. (a) Explain the properties of musical sounds

(b) Mention three categories of musical instruments and give some examples

6. (a) State the factors affecting the frequency of vibrating wire

(b) A wire of length 20cm and mass of 31.2kg is under a tension of 220N.

What is (i) Fundamental frequency (ii) The frequency of the third harmonic

stationery wave consisting of two loops is produced. Draw a sketch of a

wave and find the wavelength

7. (a) A sonometer wire of length 40cm between two bridges produce a note of

512 Hz when plunked at its middle. Calculates the length that will

produce a note of 256 Hz, if the Tension is the same

(b) The frequency obtained from a plunked string is 400 Hz when the

Tension is 2N. Calculate the

(i) Frequency when the Tension is increased to 8N

(ii) The Tension needed to produce a note of frequency 600 Hz

8. (a) Explain the property of sound in an empty hall and in a filled hall

(b) Mention four factors affecting the speed of light in air

hear her sound is 2.5seconds. Calculate the speed of sound in air

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9. (a) Define the following terms (i) Audibility range (ii) Ultrasonic sound

(iii) Infrasonic sound (iv) ultrasonic vibration

(b) When a turning fork is vibrating in a resonance tube at 20cm and 42cm. If

the frequency of the turning fork is 570 Hz. Calculate the velocity of

sound in air

10. (a) In a closed pipe the first resonance is at 216cm and the second is at

328cm. Calculate wavelength and the end correction

(b) A turning fork of frequency 208 Hz is producing the frequency in an

open pipe. If the velocity of sound in air is 340m/s. Find the length of the

tube which gives the (i) First resonance (ii) Third resonance

(iii) Fifth resonance

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CHAPTER: 2

ELECTROMAGNETISM

Electromagnetism: Is the effect produced by the interaction of an electric current with a magnetic field. The interaction can result in a force causing the conductor carrying the current to move

If, on the other hand, a force is applied to a conductor (with no current) in a magnetic field it produce a movement which can determine the current in the conductor

Consider the electric circuit below

When the switch is closed an electric current flows through the conductor to generate magnetic field around the conductor; this will cause a deflection on the compass needle in different sides

Direction of rotation of a compass needle

When a current flow due south ward a compass needle rotate towards the west (clockwise)

By allowing the current to flow Northward, the compass needle is made to point due East (anticlockwise)

If the wire is placed horizontally, the compass needle is made to point due South

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The magnetic field around a current-carrying conductor can be shown by means of magnetic field lines

Fig. Magnetic field lines in a conductor

The Pattern of the Magnetic Field Lines around a Straight Conductor

Identify the pattern of the magnetic field lines around a straight conductor

The magnetic field pattern is usually given in a plan view. A dot in circle shows that the current is coming out of the plane. A cross the circle shows that the current is moving into the plane

Plane view of a magnetic field pattern

The strength of the magnetic field depends on the magnitude of the electric current; that the higher the current, the stronger the magnetic field, and therefore the greater the deflection.

The strength of the magnetic field decreases as you move further from the conductor this is because, there will be less deflection as the compass is drawn (moved) from the current-carrying conductor.

Fig strength of magnetic field

The Direction of Magnetic Field around a Current-Carrying Conductor

The direction of the field is determined by applying two rules, these are:

1. Right-hand Grip Rule

2. Maxwell‘s cork screw rule

1. Right-hand Grip Rule

The Right-hand Grip Rule can be applied in

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(a) Straight conductor

(b) Solenoid-carrying an electric current.

(a) Right-hand Grip Rule For a straight conductor

The Rule stated that “When the wire carrying the current is gripped by the right hand with the thumb pointing in the direction of the conventional current (from positive to negative), the fingers curl around the wire pointing in the direction of the magnetic field”

Fig. Right hand rule for straight conductor

(b) Right hand grip rule for a solenoid

The Rule states that “When a right hand is wrapped around a solenoid with fingers pointing in the direction of convectional current, the thumb pointing in the direction of the magnetic North pole (Field)”

Fig. Right hand rule for solenoid

A solenoid: Is a long coil containing a large number of close turns of illustrated copper wire.

The magnetic field produced by a solenoid is similar to that produced by the bar magnet

Strength of a magnetic field produced by a current carrying a solenoid

The strength of a magnetic field produced by a current carrying a solenoid is direct proportional to the

(a) Number of turns in the solenoid

(b) The magnitude of the current flowing through the solenoid

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Maxwell‘s –Right –hand screw rule

The rule states that: “If a right-hand screw advances in the direction of the current, then the direction of rotation of the screw represents the direction of the magnetic field due to the current

Maxwell’s hand screw rule

Direction of a Force on a Current carrying Conductor in a Magnetic Field

The direction of the force on a current-carrying conductor in a magnetic field can be determined using Fleming‘s Left –Hand Rule.

Fleming‘s Left –Hand Rule

The rule states that:

If index finger, the middle finger and the thumb of the left hand are hold mutually perpendicular to each other so that the index finger points in the direction of the magnetic field and the middle finger points in the direction of current in the conductor, then the thumb will point in the direction of the force acting on the conductor

Fig. Fleming‘s Left –Hand Rule

Force due to two parallel conductors carrying Current

When the Current Flowing in the Same or Opposite Direction

The force produced into two parallel conductors carrying current depending on the direction of the two currents that

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(a) When the currents are flowing in opposite directions, the conductors repel one another. This happens because

The magnetic the fields between the conductors add up, while they cancel out on the outside. The field between them is stronger than on the outside. The resultant force is toward the outside of each conductor, hence repulsion.

(b) When the currents are flowing in the same direction, the conductors attract each another. This happens because

The magnetic field between the conductors cancel out, thus reduces the net field while on the outside, the magnetic fields add up, thus increasing the net field. Therefore, the magnetic field is weaker between the conductors than on the outside

Electromagnetic Induction

Electromagnetic Induction: Is the production of e. m. f whenever there is a change in the magnetic flux linking a conductor.

The e. m. f produced is called induced e. m. f and the resulting current is called induced current.

The Laws of Electromagnetic Induction (Lenz’s and Faraday’s laws)

The direction of induced e. m. f is explained using the following principles (laws)

- Lenz’s law

- Faraday’s

Lenz’s Law

States that: “The direction of the induced e. m. f is such that the resulting induced current flows in such a direction that it opposes the change that causes (produces) it”

From the law

1. If a magnet is passed through (North pole first) a coil of wire, the current flow in one direction

2. If the magnet is pulled away, the current flows in the opposite direction

Note: The quicker the magnet moves, the greater the deflection of the galvanometer

The results are shown below

(a) When a coil is approaching the North pole of a magnet

Here the coil or magnet will be attracted to each other

Because the current is flowing in the anticlockwise direction producing the North pole at the end of current flowing

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(b) When a current is withdrawing North pole (The magnet in N and the coil S)

The magnet is moving away from the coil. Hence the current is flowing in the clockwise direction

The magnet is moving towards a coil. Hence the current is moving in clockwise direction

(d) With drawing South pole (Current is flowing in clockwise direction)

The magnet will be moving away from a coil. Since the current is flowing anticlockwise direction.

Faraday’s Law.

States that: “The induced e. m. f in the conductor in a magnetic field is proportional to the rate of change of magnetic flux linking the conductor”

Note: Faraday’s law relates in the magnitude of induced e. m. f and the rate of change of the magnetic flux linking the conductor.

The magnitude of the induced e. m. f depends on:

1. The strength of the magnetic field

2. The rate of change of the magnetic flux (speed of motion)

3. The area of the conductor that is in the magnetic field

(Number of turns in the coil)

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Explanation from the Factors

Increasing the strength of the magnetic field increases the deflection of the galvanometer connected to it

Increasing the speed (V) increases the deflection of the galvanometer

Increasing the area (Number of turns) increases the deflection of the galvanometer

Necessary conditions for the production of induced current

1. There should be a flux linkage change with time (within a time)

2. The conductor should be a part of a closed system

Self and Mutual (together) Induction

Self induction: Is the effect in which the e.m.f is induced due to the change of current in the same coil. Or Is the production of emf due to change in current in the same coil.

Is the production of e.m.f in a conductor as a result of changing (increasing or decreasing) current in the same conductor

Mutual Induction

Mutual Induction: Is the production of e.m.f in one conductor as a result of changing (increasing or decreasing) current in another conductor

When current is flowing through the conductor it varies (it increase or decrease) and creates a varying magnetic field that cuts across the conductor. That produce the voltage called voltage back e.m.f that, tends to limit or reverse the original current.

Therefore the obtained results are as follows:

a) Increasing current → e.m.f is induced

b) Decreasing current → e.m.f is induced

c) Constant current → no induced e.m.f

If two coils are placed near each other, a varying current in one coil will induce a current in the other. Hence this explains the so called mutual induction. And the coil that provides current is called the primary coil while that in which a current is induced (received) is the secondary coil

Note: The e.m.f induced in the secondary coil is proportional to the rate of change of the current in the primary coil. S.e.m.f α P.current/time

In the diagram bellow the current in the primary coil produces a magnetic field but the current is constant, hence there is no electromotive force (e.m.f) and no current in the secondary coil

Note: When the current in the primary coil is increased the magnetic flux increases in

secondary coil and produce the following in secondary coil

1. Increasing magnetic flux

2. Increases in e.m.f

3. Producing current in opposite direction

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Note: When current in primary coil is decreased cause the decrease in magnetic flux in secondary coil. Hence the following are produced in secondary coil

1. The e. m. f is Induced

2. The current is induced that turn back

3. Magnetic field is induced in the same direction

The Induction Coil

The Induction Coil: Is an electrical device consisting of two coils, the primary coil and the secondary coil, wound one over the other on an iron core.

Uses of induction coil

It is used to produce high-voltage alternating current from low-voltage direct current.

The primary coil is made up of tens or hundreds of turns of coarse wire while the secondary coil consists of thousands of turns of fine wire. The secondary coil is wound on top of the primary coil

Fig. Induction coil

Mode of action of induction coil

The D.C in the primary coil is switched on and off by a make-and-break mechanism, that produce changes in current and magnetic fields which are necessary for electromagnetic induction to occur which produce higher voltage in the secondary coil

Note: QN: When the Induction coil is required to be used

It can be used when a high voltage is required from low voltage direct current source

Note: The induced e.m.f is very large, usually in the order of hundreds of kilovolts

(kV). Such a high voltage is achieved because of two things:

1. The secondary coil has a large number of turns compared to the primary coil.

2. The rapid change in the primary current when it is switched on and off causes a

rapid in the magnetic field through the secondary coil.

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Applications of the induction coil

1. It is used in the ignition system of internal combustion engines

2. It is used to trigger (cause) the flash tubes used in cameras and strobe (device that

produce) lights

3. It is also used in wireless telegraphy (device that send message by wind waves)

Generators

Generator: Is a device that uses a coil of wire rotating in an external magnetic field to produce either an A.C or D.C Or

Is the device which produces electricity on the basis of electromagnetic induction by the continuous motion of either a coil or a magnet

A.C Generator or alternator

An a.c generator utilizes (use) Faraday‘s law of induction, spinning (rotating) a coil at a constant rate in a magnetic field to induce an oscillating e.m.f

The A.C generator consists of an armature made up of several turns of insulated wire wound on a soft-iron core. The armature revolves freely on an axis between the poles of a powerful magnet. Two slip rings are connected to the ends of the armature and two carbon brushes rest on the slip rings

Fig. A simple A.C generator

Note: When the coil is vertical, no cutting of the magnetic lines of force takes place although the number of lines linking the coil is Maximum. Hence the rate of change of magnetic flux is zero and as a result, no e.m.f is induced in the coil.

When the armature is parallel to the magnetic field, the rate of change of magnetic flux is Maximum and the motion of the coil is perpendicular to the magnetic field, hence an e.m.f is induced along the sides of the coil

D.C generator

It is made by replacing the slip rings in the arc generator with a commentator. Each half of the commentator ring is called a commentator segment and is insulated from the other half. Each end of the rotating loop of the wires connected to a commentator segment. Two carbon brushes connected to the outside circuit rest against the rotating commentator.

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Fig. D.C generator

Transformer

A transformer: Is a device used for stepping up or down the alternating voltage. or

Is the device that uses mutual induction between two coils to convert an a.c across one coil to a larger or smaller A.C across the other coil.

A transformer is made up of two coils, each with a different number of loops linked by an iron core so that the magnetic flux from one passes through the other. When the flux generated by one coil changes the flux passing through the other will change, inducing a voltage in the second coil.

The coil that provides the flux that is the coil connected to the A.C power source is known as the primary coil while the coil in which the voltage is induced is known as the secondary coil

When the number of turns in the primary coil (N) is lower than the number in the secondary coil (N), the secondary voltage will be higher than the primary voltage. This is called the step-up transformer. The opposite of this is called the step-down transformer.

Examples of devices that operates on the principle of mutual induction

(a) The induction coil

(b) Transformer

Transformer equation

It is showed that the e. m. f in a transformer coil is proportional to the number of turns

Therefore

Vp Np and Vs Ns

Vp = Np, Vs = Ns

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This is the relationship between the primary and secondary voltage and number of turns

If loss of power is neglected, the power in the primary is equal to that of secondary coil

Ip x Vp = Is x Vs

= This is the general transformer equation

Transformer efficiency

Is the ratio between the output power (power in secondary to the input power (power in primary)

Example 1: A transformer is used to step down 240V mains supply to 12V for laboratory use, if the primary coil has 600 turns. Determine the number of turns in the secondary coil

Data Information

Vp = 240V, Vs = 12V, Np = 600turns, Ns = ?

From the general equation

= is satisfactory

Ns = = 30turns

Number of turns in secondary is 30 turns

Example 2: A step up transformer has 10,000turns in the secondary coil and 10turns in the primary coil, an A.C of 5Aflows in the primary circuit when connected to 12V A.C supply.

(a) Calculate the voltage in the secondary coil

(b) If it has an efficiency of 90%, what is the current in the secondary coil

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Data Information

Ns = 10,000turns, Np = 100turns, Ip = 5A, Vp = 12V, Vs = ?

(a) From

Vs = =

Therefore voltage in secondary is 1200V

(b) From Power = current x Voltage

P = IV

Power in primary = Ip x Vp = 5 x 12 = 60W

But

0.9 = , Ps = 54W

Power in secondary is 54W

From Ps = IsVs

Is = = = 0.045A

Therefore current in secondary is 0.045A

Example 3: A transformer with primary and secondary windings of 200turns and 100turns respectively is connected to 250V mains. Calculate the secondary voltage if the transformer is 75% efficiency

Data information

Np = 200turns, Ns = 100turns, Vp = 250V, Vs = ?

From or

Hence is applicable

Vs =

Voltage in secondary is 94V

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Uses of transformers

Transformers are used in power stations to step up voltage for transmission from the station to the areas of consumption (appliances)

Note: The losses due to resistance are reduced by stepping up the voltage, hence it reduces current when power is reached to the area of consumption it is stepped down to the value required for the domestic use

Condition for an Ideal transformer

For an ideal transformer input power to the transformer is equal to the output power from the transformer means that Power in primary coil = Power in secondary coil

IpVp = IsVs

In any practical transformer the efficiency is not equal to 100% this is because there is power dissipated as heat which leads to power losses in the transformer

Types of losses in transformer

Copper losses: Are loss of power in primary winding in the form of heat due to resistance in primary coil

Iron losses: Are due to the heat occurring in the iron core caused mainly by eddy (current obtained by varying magnetic field) current

Advantage of using A.C over D.C in electric power transmission

An A.C is used more often than D.C power transmission this is because its voltage can be varied (increased or decreased) according to the required power rating.

REVIEW QUESTIONS ON CHAPTER - 2

1. (a) What are Electromagnetism (ii) Induced current

(b) (i) List the necessary condition for production of induced current

(ii) Explain why magnetic field is stronger at the centre than at its edge

2. (a) Consider the diagram below

(i) What are the poles represented by letter A and B? Explain

(ii) Is the magnet attracted to the coil or not? Explain why

(b) (i) Differentiate between self-Induction and mutual induction

(ii) What is an Induction coil? When an induction coil is said to be used

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3. (a) (i) How is a d.c generator be converted into an a.c generator

(ii) What are the ways of increasing the induced e.m.f in a coil

(b) (i) The direction of force on the current carrying conductor in a magnetic field

can be determined by _________________. State the rule and draw the

diagram showing all the directions required

(ii) The force produced into two parallel conductors carrying current depends

on the flow of current in opposite and the same direction. Draw the diagrams

showing their results

4. (a) (i) Define electromagnetic field

(ii) Show electromagnetic field lines pattern in a solenoid

(b) (i) State the advantages of using a.c generator over a d.c generator

5. (a) (i) What is transformer (ii) With symbols what are the transformers

(b) A d.c generator has a resistance of coil of 10Ω and is connected to a bulb of

100Ω. Calculate the induced e.m. If the current flowing in the bulb is 5A

6. (a) (i) State an ideal transformer. Why in any practical transformer its efficiency is

not equal to 100%

(ii) Two losses in transformer are. How may be reduced

(b) A transformer with primary and secondary windings of 250 and 120turns

respectively is connected to 240V mains. Calculate the secondary voltage if a

transformer is 90% efficiency. Is a transformer step-up or step-down? Why

7. (a) (i) Could a transformer be used to increase the voltage of the battery. Explain

(ii) A low voltage outdoor-lighting system uses a transformer to step down the

240V to 24V. The lighting system has 6lamps with a total resistance of 9.6Ω.

What is the current in the secondary and primary coil

(b) Briefly explain why the core of a transformer is made of thin layers of metal

insulated from one another

8. A 20W lamp with a resistance of 5Ω uses a power supply from the secondary coil of a transformer. If the primary coil is connected to a 100V a.c outlet

(a) What is the current in the lamp when it is switched on

(b) What is the secondary voltage

(d) What type of transformer is it? Why

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CHAPTER: 3

RADIOACTIVITY

RADIOACTIVTY: Is the process for unstable atoms to emit rays naturally or artificially.

For an element to emit rays should be unstable. The stability of an element decrease with the increase in atomic number for, example sodium (Na) with atomic 11 is stable compared to Radon (Rn) with atomic number 86. The element is unstable; because of having weak strong force called Binding Energy

Binding energy : I the energy required by an element to separate neutrons and electrons from the nucleus of an atom. Or is the mechanical energy required to disassemble a whole into separate part. The unstable nucleus (nuclei) loss protons and neutron as they try to become stable

Radioactive element: (Materials) Are elements or materials having the ability of emitting rays. Sometimes are called radioactive Substances. Examples of radioactive substances Radon ²²²₈₆Rn, Radium ²²⁶₈₈Ra, Thorium ²³⁰₉₀^Th, Uranium ²³⁶₉₂U, Lead Pb

Radioactive decay: Is the process by which an unstable nucleus loss energy in form of particles or electromagnetic waves when emitting rays. The energy produced is in two forms namely Particles and electromagnetic waves

The Particles includes

1. Alpha (α) with positive charges (+) and Are called particles because

2. Beta (β) with negative charges (-) they possess charges

3. Electromagnetic waves include only Gamma ray (γ) Ray or Radiation

Note: The alpha and beta rays are called particles because they possess charges while gamma is not a particle because it does not possess any charge.

Nuclear radiations Are radiations produced by radioactive substances or elements or materials by radioactivity on becoming stable

The radiations are

§ Alpha radiation/rays/Particle (α)

§ Beta Radiation/rays/Particles (β)

§ Gamma ray/Radiations (γ)

Alpha Particles (α) Are helium (He) nuclei generated from nuclear disintegration

Beta Particles (β) Are electrons (⁰_-1e) produced from the nuclear of disintegration

Gamma ray/Radiations (γ) Are electromagnetic waves generated when an unstable nuclide disintegrate to form smaller nuclei

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Production of Radioisotopes (Radiations)

The radiations are produced in the lead shield as shown below

Figure production of radioisotopes

Penetrating power of the three types of radiations (α, β & γ)

Figure Penetrating power of the three types of radiations

Effects of electric field on the three types of radiations

Figure effect electric field on the three types of radiations

Properties of the three radiations

Properties of alpha particle (α)

The emission of alpha particle by an unstable atom is called alpha decay

1. Is a helium in nature (⁴₂He)

2. It is composed of two protons and two neutrons

3. It carries positive charges (+2)

4. Travel with low speed hence low penetrating power

5. Can be stopped by a sheet of paper

6. Can be deflected by both magnetic and electric field

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7. Has higher mass

8. Affects photographic plates

Properties of beta particle (β)

A beta particle is an electron ejected from a radioactive nucleus that has an excess of neutrons

1. Is an electron in nature (⁰_-1e)

2. It carries a negative charge (-1)

3. Travel with high speed hence high penetrating power

4. Can be stopped by aluminium sheet (foil)

5. Can be deflected by both magnetic ad electric field

6. Has low mass

7. Affects photographic plates

Properties of gamma ray (γ)

Gamma is not a particle because of having no charge but it is an electromagnetic waves. It is usually released during the emission alpha or a beta particle with the excess of energy

1. Is an electromagnetic wave in nature

2. Has no charges

3. Travel with intense (very high) speed hence very high penetrating power

4. Can be stopped only by Lead shield blocks (Materials)

5. Cannot be deflected because of having no charge

6. Has no mass

7. Affects photographic emulsion

Radioactive detectors

These are practical instrument used to detect the three types of radiations (α, β and γ) based on the ability to ionise atoms or molecules of a gas through which they pass.

The common devices are

§ Geiger-Muller tube (GM tube)

§ Spark counter

§ Cloud chamber (Wilson cloud chamber

§ Geiger-Muller tube (GM tube)

Is the sensitive device compared to the other detecting Beta particles

It consists of a hollow tube filled with a noble gas like argon. At one end has a thin window made by mica through which the radiations enters the tube and cause the

radiations to be ejected from the gaseous atom (argon gas) and are then accelerated to the positively (+vely) charged collector wire and produce a brief pulse of electric current. The pulse produced can cause a Click in a speaker or be counted by a scalar.

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Figure Geiger Muller tube

§ Spark counter

The counter consists of a piece of wire gauze and a long straight wire separated by few centimetres of dry air and connected to a high voltage power supply. The power supply is adjusted to a voltage below the level required to cause the spark, when the radioactive source is brought near the device the radiation partially ionises the air between the gauze and the wire. This increases the air׳s conductivity allowing a spark of electricity to jump from the gauze to the wire. Hence the alpha (α) particle is detected

Figure the Spark counter

§ Cloud chamber (Wilson cloud chamber)

When the radioactive source is brought near the chamber they leave the trail of charged particles (ions). Hence the tracks are indicated with distinct shapes as alpha particle that is broad, Straight, and thicker and or beta particle that is thinner and dotted. The more features can be determined by magnetic or electric field

Figure Cloud chamber

The other radioactive detectors

§ Photographic Film

§ Bubble chamber

§ Gold leaf electroscope

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Effects of radiations on the nucleus of an atom

Effects of alpha particle

When a radioactive nucleus emits alpha particle the following occurs

v The atomic number of the atom or element decreases by two (2)

v Atomic mass of the element decreases by four (4)

Note: Hence the atomic number of the new element determines what element is present. Hence generate a law called the law of alpha emission (The 1^stlaw of Radioactivity)

1^St Law of Radioactivity

States that “When the nucleus of an atom disintegrate (breakdown) with the emission of alpha particle it become two element above in the periodic table”.

The process is represented as ^A_ZX ^A-4_Z-₂Y + ⁴₂He

^A_ZX Represent the parent nuclide notation

^A-4_Z-₂Y Represent the daughter nuclide notation

⁴₂He Represent the emitted radiation

Example1: Uranium - 238 undergoes an alpha decay to produce thorium show its disintegration.

From

^A_ZX ^A-4_Z-₄Y + ⁴₂He(emission of alpha particle)

²³⁸₉₂U ^238-4_92-2Th + ⁴₂He ( α - emission)

²³⁸₉₂U ²³⁴₉₀Th + ⁴₂He ( α - emission)

For Radium

²²²₈₈Ra ²¹⁸₈₆Rn + ⁴₂He ( α - emission)

§ Effects of Beta particle

When an atom emits Beta particle the following may occur

v A neutron split into a proton and an electron

v The electron is emitted while protons remain in the nucleus

Hence the results are

v The increase by one in the number of proton

v The decrease by one in the number of neutrons

v Atomic number of a new element is increase by one

v Beta decay has no change (Effects) in the mass number

The decay equation is ^A_ZX ^A_Z-1Y + ⁰_-1e (β- emission)

During this process the 2^nd law of Radioactivity (the law of β – decay)is generated

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The 2^nd law of Radioactivity

States that “When the nucleus of an atom decay by the emission of beta (β) particle it becomes one element latter (below) or ahead in the periodic table”

Example 2: Carbon undergo β-decay produce nitrogen as below

From ^A_ZX ^A_Z-1Y + ⁰_-1e (β- emission)

¹⁴₆C ¹⁴₇N + ⁰_-1e (β- emission)

§ Effects of Gamma radiations

Gamma rays are produced during the production of alpha or beta particle. The excess energy in the daughter nucleus results in the release in the gamma rays Hence the emission of gamma rays has no effects in the nucleus of an atom then it does not alter the composition of the nucleus i.e. The mass and atomic number of an atom does not change.

The decay equation is ⁶⁰₂₇co ⁶⁰₂₇co + ⁰₀γ(γ – emission)

Example 3: A radioactive nucleus is denoted by the symbol ²⁸⁸₉₂x. Write down the position of the nucleus at the end of each of the following stages of disintegration

(i) The emission of α – particle (ii) Emission of beta particle

(iii) Emission of some gamma rays

Solution

(i) ²⁸⁸₉₂x ⁸⁸₉₂Y + ⁴₂He (α – emission)

(ii) ²⁸⁸₉₂x ⁸⁸₉₃Z + ⁰_-1e (β- emission)

(iii) ²⁸⁸₉₂x ²⁸⁸₉₂W + ⁰₀^γ(γ – emission)

Example 4: What are the values of z, y and z in the following

Equations (i) ^x₈₈Ra ²²²₈₆Rn + 4_yz (α – emission)

(ii) ^x_yTh ²³⁴₉₁Pa + ⁰_ze (β- emission)

Solution

(i) x – 222 = 4, x = 226

(ii) From ⁴₂He = 4_yz, y = 2 and Z = He

Example 5: A radioactive nucleus is denoted by the symbol ²²⁶₈₈W write down the composition of nucleus at the end of the following stages of disintegration

(i) Emission of α – particle (ii) Further emission of a beta (β)-particle

(iii) Further emission of gamma (γ) - ray

Solution

(i) ²²⁶₈₈W → ²²²₈₆X + ⁴₂He (α – emission)

(ii) ²²²₈₆X → ²²²₈₇Y + ⁰_-1e (Further β- emission)

(iii) ²²²₈₇Y → ²²²₈₇Y + ⁰₀^γ(Further γ – emission)

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Example 6: A radioactive nucleus is denoted by the symbol ²²²₈₆N write down the composition of nucleus at the end of the following stages of disintegration

(i) Emission of α – particle (ii) Emission of two α-particle

(iii) Emission of two beta (β)-particle

Solution

(i) ²²²₈₆N → ²¹⁸₈₄M + ⁴₂He (α – emission)

(ii) Two α-particle = 2(⁴₂He) = ⁸₄He

²²²₈₆N → ²¹⁴₈₂L + ⁸₄He (α – emission)

(iii) Two beta (β)-particle 2(⁰_-1e) = ⁰_-2

²²²₈₆N → ²²²₈₈P + ⁰_-2e (two β- emission)

Types of radioactivity

(i) Natural radioactivity (ii) Artificial radioactivity

(i) Natural radioactivity: Is the types of radioactivity in which the emission of rays occurs naturally

Applications of natural radioactivity

The natural radioactive isotopes have much field application in different areas such as

Ø In Medicine, In Industry, In Agriculture, In Science

In medicine: In medicine radioisotopes are used in medicine for diagnosis and treating illness. They are particularly used as tracers in certain diagnostic procedures because they are chemically identical with stable isotopes of the same element and they can be readily traced even in minute quantities with detection devices.

Examples of most tracers Iodine – 131 and – Phosphorus

In Industry: -

-Are used to measure and control the thickness or density of metal and plastic sheets

-To preservation of foods by killing microorganisms that cause Spoilage.

In Agriculture:- They are used to induce mutation in plants to develop superior varieties that are harder and more resistance to diseases

In science:- They are used in radiometric dating to determine the time for decaying in elements (Radioactive substances) by Carbon- 14.

(ii) Artificial radioactivity (Induced Radioactivity)

Is the types of radioactivity in which the emission of rays occurs artificially.

Means the elements are bombarded with sub-atomic particles or high energy such as

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X-rays and Gamma rays.

The materials in which radioactivity is induced is called Target nucleus while the Bombarding material is called Projectile

Kinds (Methods) of Inducing Radioactivity

· Neutron activation

· Photonuclear reactions

Neutron activation:- In this the element emit rays after educed with the materials and the nuclear capture free neutron becoming heavier and unstable. Hence it decay and emit particles like (α, ¹₁n, ¹₀n)

Photonuclear reactions:- In this process the targeted nucleus is bombard by higher energy of X-rays and Gamma rays.

Application of artificial radioactivity

(i) It is used (applied) in nuclear reactors for nuclear energy and makes nuclear bombs

(ii) It is used to shorten the life time of and level of radioactive substances

(iii) It is used to limit the effects of radioactive substances. Hence a non destructive

analysis method .

Effects of nuclear radiations (α, β and γ)

(i) Can cause injury to the skin depends on the dose and condition of exposure

(ii) Higher dosage affect the blood forming cells in bone marrow, causing depressing

of blood cells and or Haemorrhage.

(iii) Affect immature sperm-forming cells while mature are resistant to radiation in

reproductive organs

(iv) Affect eyes causing opecification of the lens for months

(v) Affects the growth and development of the embryo

(vi) Affects brain and sensory organs

(vi) Cause incidence of cancer for

· Atomic bomb survivors

· Radiation workers

· Some patients exposed to radiations for medical purposes

Precautions to be taken from the hazards of radiations

a) By limiting the time of exposure

b) Increasing the distance from the source of radiation. Eg 12cm for Alpha (α) particle

c) Using the absorbing materials. Eg Aluminium sheets (Foil) for beta particles

d) The radiation sources should be kept in lead materials and out of living environment.

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e) The package should be labelled appropriately, handled carefully and use dosimeter to detect them.

Dosimeter:- Is a device used to detect/measure the presence and level of radiation to the environment

Nuclear Fission:- Is the process in which an unstable atomic nucleus splits into two or more nearly equal small nuclei and a lot of energy in form of heat.

It produce energy because it exothermic reaction

Eg ²³⁶₉₂U → ⁹⁴₃₆Kr + ¹⁴⁰₅₆Ba + 2(¹₀n) + Energy

Or it may show a chain reaction

⁹⁹₄₁Nb β ⁹⁹₄₂Mo β ⁹⁹₄₃Te β ⁹⁹₄₄Ru (Stable)

²³⁶₉₂U

¹³³₅₁Sb β ¹³³₅₂Te β ¹³³₅₃ I β ¹³³₅₄Xe β ¹³³₅₅Cs

(Stable)

Application of nuclear Fissions

(i) It is used to generate electricity in nuclear power plants.

(ii) It is used in making nuclear bombs

Nuclear Fusion:- Is the process in which lighter nuclei join (fuse) together to form a heavier nucleus.

It is accompanied by releasing or absorbing of energy

Eg. ²₁H + ³₁H → ⁴₂He + ¹₀n + energy

Deuterium Tritium

The fusion of two nuclei lighter than Iron or Nickel release energy

While The fusion of heavier nuclei than Iron or Nickel absorbs energy

Application of nuclear Fusion

(i) It is used in fusion power plants to generate electricity

(ii) It is used to make nuclear weapons Eg. Hydrogen bombs

Half life (t_1/2) Is the time taken for half of its atom to decay (disintegrate)

The SI unit of half life is the same as the Units of Time hence it maybe a Second, Minute, Hour, Day, Year

Eg. The half life of a certain sample is 36minutes

This means that a sample it takes 36 minutes for half of it sample to decay (disintegrate) and become stable nuclei.

When a sample disintegrate the following constants are happening

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· The number of initial sample (Ni):- This is the original number of sample before disintegration Eg. 3000gram, 5600perminute

· The number of final sample (Nf):- This is final (The remaining) number or amount of sample after disintegration

· Time taken (T):- This is the time used for a sample to disintegrate from original to final.

· The half life (t _1/2):- This is the time taken for half of its atom to decay

Note: The SI Unit of Time and half life Must be the same and that of Initial and Final samples Musts also be the same at any condition.

Half life formula is ⁿ

Where n = T/t_1/2

The number of Fractions remaining un-decayed = Nf/Ni or

(1/2) ^T/t1/2

Activity Is the number of nuclei disintegrated per unit time

Activity = Number of nuclei disintegrated

Time taken

Thermonuclear Fusion:- Is the process of using extremely high temperature to bring about fusion of an atom.

Background count Is the ionizing radiation present in our environment due to emission from their sources.

The background radiation sources includes

· The outer space.

· Radioactive rocks inside the earth.

Example 7. A sample initially contains 120g with the half life of 36sec.It decays after 72seconds (a) What mass of it remained un-decayed (b) What fraction of the sample remains un-decayed

Data given Initial sample (Ni) = 120g, Final sample = ?,

Time taken (T) = 72sec, Half life (t_1/2) = 36sec

(a) From Nf/Ni = (1/2)^T/(t
1/2)

Nf/120 = (1/2)^72/36, Nf/120 = (1/2)², Nf/36 = 1/4

Nf = 120g/4 = 30g

The mass remaining unchanged (Nf) = 30g

(b) Fraction remaining = Nf/Ni = 30g/120g = 1/4

The fraction remaining (Fr) = 1/4

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Example 8. A particular radioactive source has a half life of 2hours. A sample gives a count 2400persecond at 11:00Am when does a count dropped to approximately 300persecond in the same counting system.

Data given (t½) = 2hrs, Ni = 2400/sec, Nf = 300/sec, T = ?

From Nf/Ni = (½)^T/(t½)

300/2400 = (½)^T/2, 1/8 = (½)^T/2, (½)³ = (½)^T/2

3 = T/2, T = 6hours

The time taken is 6hours. Hence From 11:00Am + 6hrs = 1700hrs

The count will ends up 300/sec at 5: 00Pm

Example 9. The half life of a certain sample is 24days. If its activity is 4x10⁵ disintegration per second. 72days later the activity of this thorium sample will be?

Data given t_½ = 24days, T = 72days, Ni = 400000dis/sec, Nf = ?

From n = ^T/(t½), n = 72/24 = 3, n = 3

Nf = (½)ⁿ, Nf = (½)³, Nf = 1 , Nf =50000dis/sec

Ni 400000 400000 8

After 72 days later the sample will be 5x10⁴ = 50000dis/sec

Note: By using half life formula one of the constants data may be calculated by making it as the subject

REVIEW QUESTIONS IN CHAPTER: 3

1. (a) Give the meaning of the following as applied in radioactivity

(i) Element (ii) Atom (iii) Atomic number (iv) Mass number (v) Neutron number

(b) Write down the three sub-atomic particles by stating where they are found and

give their charges

2. (a) Define the following (i) Isotopes (ii) Isotopy

(b) Write down the names of the isotopes of hydrogen

3. (a) Differentiate between Natural and Artificial radioactivity

(b) What is radioactive decay (c) With two examples what is Radioactive substance

4. (a) With two properties what are

(i) Alpha particle (ii) Beta particle (iii) Gamma ray

(b) Explain why gamma is not a particle

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field but not gamma

5. (a) Consider the diagram below

Questions

(i) What does latter A, B, C, D, E, F. Represents?

(ii) What amount of Volts is supplied by the figure

(iii) Explain why latter B and C are attracted to that and not D

(iv) What is the purpose of the figure above?

(b) Give one effect for each of the following radiations alpha, beta and gamma in the

nucleus of an atom

7. (a) With 1 example explain Nuclear Fission and Nuclear Fusion

(b) Give two applications of the nuclear stated in (a) above

(i) ^x₈₈Ra → ²²²₈₆Rn + ⁴_yK (it is emission of......? )

(ii) ²³⁴₉₀Th → ²³⁴₉₁Pa + ^x_yK (it is emission of......? )

8. (a) A radioactive nucleus is denoted by the symbol ²²⁸₈₈W write down the

composition of nucleus at the end of the following stages of disintegration

emission

(i) alpha (α) particle (ii) Beta (β) particle (iii) Gamma (γ) radiation

(ii) What is Half life (iii) where is the source of background radiation

(b) The half life of Uranium is 24days. Find the (i) Mass remaining

unchanged (ii) The fraction remaining to its original substance for 120g of the

substance after 144days

9. (a) A radioactive substance with 2048perminute decaying to 32perminute. If the

half life is 3minutes calculate

(i) The time taken

(ii) The fraction remaining unchanged

(b) The half life of a substance is 4days what does this mean

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Time in days	0	8	16	24	32	40
Mass in kg	80	60	40	28	20	14

xxxxxxxxxxxxxxxxxxxxxxx

CHAPTER: 4

THERMIONIC EMISSION

Thermionic emission:- Is the escape (discharge) of electrons from a surface of a heated material.

The discharge of electrons from heated materials depends on temperature. Means the increase in temperature also there is the increase in electrons and vice verse. If a metal is heated electrons gain K.E and escape from a heated to un heated metal surface (from high to low temperature) to the environment or surroundings by the thermionic emission method.

Cathode rays:- Are streams of fast moving electrons in a specific directions

Productions of cathode rays

Cathode rays are produced in the cathode ray tube. Then are

accelerated and focused to the screen through the GRID, X and Y

plates. An image is formed when electrons strike the screen. The

deflecting plates (X and Y plates) Position the beam on the screen.

The cathode ray tube:- Is the vacuum tube used to produce the

cathode rays ` Figure cathode ray tube

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Properties of cathode rays

1. They travel in a straight line with the speed nearly equal to that of light

2. They carry negative charges

3. They are deflected in both magnetic and electric field

4. They affect photographic plate

5. They produce X-Rays when suddenly stopped

6. They carry energy and momentum

Applications of cathode rays

1. They produce X- Rays

2. Set a paddle wheel into motion when it is placed in the path of these rays

3. Heat the object only which they fall.

The Cathode ray tube is evacuated so that electrons travel without colliding with other particles.

The gas in the CRT is not maintained to make it not conduct with an electric sparks when pd across it as it happens in open air. Hence the image will not be formed on the screen because the cathode ray will not be there. So the predictable image will not be shown on the screen.

The cathode rays carry negative charges, when electric and magnetic field are placed near the CRT the electron beam deflect to the Positive terminal then to the North pole of the of the electric and magnetic field respectively

Places where cathode ray tube is applicable

It is applied in

(i) Television

(ii) Computer display

(iii) Cathode ray oscilloscope (CRO)

· Television:- In the black and white television the image is formed on the screen by varying the Brightness at thousands of points on the screen

- The brightness of a point on the screen depends on the number of electrons

that strike it.

- The Intensity of the electron beam can be varied by changing the voltage on the

control GRID. This is done because the GRID has negative charges and so

repels the electrons coming from the cathode. Hence by changing the GRID׳S

voltage it allows more or fewer electrons to pass onto the anode then to the

screen.

· Computer display:- Work in the same way as the television

· Cathode ray oscilloscope (CRO)

The cathode ray oscilloscope operate in a similar way as a television

It is typically used to display signals in a waveforms; The signal to be studied is first amplified (Rises) then applied to the Y-plates to deflect the beam vertically at the

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same time the Voltage is applied to the X-plate to deflect the beam horizontally at a constant rate. The signal applied to the Y-plate is displayed on the screen as a function of time.

The horizontal axis serves as the uniform time scale.

The screen is converted with GRID to facilitate measurement.

The C.R.O contains three main parts which are

1. Electron gun

2. Deflecting system

3. Fluorescent screen

1. Electron gun:- It consists of Cathode and anode

2. Deflecting system:- Is consists of the X and Y-plates

3. Fluorescent screen:- It is used to emit (display) light when the electrons strike it

Figure Main Features of the cathode ray oscilloscope (CRO)

Function of the parts of CRO

1. Cathode:- It is metal filament used eg. Tungsten heated at high temperature by either direct or indirect (electric current or heating element/metal) hence electrons are produced at this part

2. Anode:- It is a metal disc maintained at high voltage used to accelerate and focus the electrons ejected from the cathode to make sure that the electrons do not accumulate at the source (cathode) and the CRO should have the Focusing anode to focus the electron reach the target (Screen) undeviated.

Note: In some tubes there is a negatively charged grid called control grid (G) located between the cathode and anode used to limit the amount/number of electrons in the beam.

The cathode and anode are correctively known as electron gun

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Note: Thus a small voltage on the grid can be made to control a much larger voltage on the anode. This is the principle used in vacuum tubes to amplify electrical signals.

3. Deflecting plates:- This consists of horizontal (X) plates that deflects electrons

horizontally (back and forward) / left or right the beam is attracted to the positive and repels to the negative plate and the vertical (Y) plate that deflects the electrons vertically (up and down). This part directs the electrons to the screen

Note: In some devices the electrically charged plates are replaced by poles of electromagnets

4. Fluorescent screen:- It is used for displaying the electrons when strike on it and form the image on striking at any point on the screen.

It is coated with phosphor so as to emit light when electrons strike it.

Applications (uses) of the cathode ray oscilloscope (C.R.O)

· It is used to measure frequencies

· It is used to measure voltage

· It is used to measure phase differences

· It is used to measure small time intervals

X-Rays:- Are electromagnetic waves produced when the fast moving electrons strike the metal target and lose energy. Or

Are unknown rays with the nature of electromagnetic radiation with higher frequency and shorter wavelength

Productions of X-rays

X- rays are produced in the X-ray tube when the fast moving electrons strike (hit) the target release the energy and being converted to X-rays.

The energy and Heat is released when X-rays are produced

Note: Little energy is converted to X-rays the rest is transferred to heat.

Figure X-Ray tube (XRT)

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Types of X-Rays

(i) Soft x-rays (ii) Hard x-rays

(i) Hard x-rays:- Are x-rays of shorter wavelength, produced at high voltage

and have high penetrating power.

They have high penetrating power hence high energy. Because of having high penetrating power the velocity of the produced electrons to strike the target is also high.

(ii) Soft x-rays:- Are x-rays of longer wave length, produced at low voltage and have low penetrating power.

Hence they have less energy to strike the target.

16. Linear Physics Form Four

Differences between hard and soft x-rays

Hard x-rays	Soft x-rays
Have shorter wavelength (high frequency)	They have longer wavelength
They have higher energy	Have less energy
They have higher penetrating power	Lower penetrating power
Produced by higher accelerating potential	Produced by lower accelerating potential
Have higher velocity	Have lower velocity

Properties of x-rays

1. They are electromagnetic waves in nature

2. They carry no charge

3. The y travel in a straight line

4. They readily penetrate matter

5. They have no effects on magnetic and electric field

6. Can be detected by photographic emulsion

Application of x-rays

1. Are used in medical field to detect broken or fractured bones or some diseases

in soft tissues

2. They are used in cancer treatment by distracting the diseased tissue

3. Are used for studying the arrangement of atoms in solids

4. Are used to study the composition of the sample

5. Are used to inspect metal casting and welded joints for hidden faults

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REVIEW QUESTIONS IN CHAPTER 4

1. (a) What is meant by thermionic emission

(b) State necessary and sufficient condition for the thermionic emission to occur

temperature

2. (a) What are cathode rays

(b) With the aid of a well ladled diagram explain how cathode rays are produced

3. (a) Cathode ray tube is used in the screen or computer and in cathode ray

oscilloscope fill the blank space

(i) In the black and white television the image is formed on the screen by...........

(ii) The brightness of a point on the screen depends on...........

(iii) The intensity of the electron beam can be varied by...........

(b) Cathode ray relate with which kind of radioisotopes

4. (a) Draw the C.R.O and give the uses of the main three parts

(b) What are the uses of the control grid in the C.R.O

electromagnet show where does the electron beam be deflected

5. (a) (i) Explain why cathode ray tube are evacuated

(ii) What happens in the C.R.T when a gas is maintained?

(b) In the production of x- rays what are the roles of

(i) Low voltage (ii) High voltage (iii) Tungsten target

6. (a) By means of a well labelled diagram describe the electric and magnetic effects

on the cathode beam deflection in the C.R.O

(b) What method in C.R.O using thermionic principle ensures that the electrons

produced

(i) Do not accumulate at the source

(ii) Reach their range undeviated

(iii) Travel without meeting other forms of particles on their way to the target

7. (a) (i) What is X- rays

(ii) Differentiate two types of x-rays

(b) (i) Give the properties of x-rays

(ii) Give four applications of x-rays

(iii) Give the areas where x-rays are applied

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CHAPTER: 5

ELECTRONICS

ELECTRONICS:- Is the branch of physics which deals with the emission and effects of electrons in materials. Or

Is the branch of science that deals with the study of flow and control of electrons (electricity) and the effects in materials

The materials are Conductors, semiconductors, insulators, vacuum and gasses

Electronic systems/circuits are made up of different components that are connected to each other to perform some tasks

Uses of Electronic Circuits

1. They are used in converting and distribution of electric power

2. They are controlling and processing of date

Types of electronic components

(i) Passive components

(ii) Active components

(I) Passive components: Are those components that consume only but do not produce energy

Why: Because

(i) They do not have the ability to produce gain

Means: They can’t increase the power or amplitude of the signals

(ii) They do not have directionality

Means: they operate in the same way regardless of the flow of current

Examples of passive components

1. Power sources (Generator, Battery

2. Resistors

3. Capacitors

4. Inductor

(II) Active components: Are components that have direction and or capacity to produce gain

Note: Generally active components are called semiconductors

Examples of active components

Diode, Transistor, Integrated circuit

CONDUCTORS

A conductor: Are objects or type of materials that allows the flow of electric current in one or more directions

For example, a wire is an electrical conductor that can carry electricity along its length

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Why conductors conduct electric current?

Because they have majority number of free electrons

How conductors produce electric current

They produce electric current when the potential difference (p.d) is connected across its terminals they force electrons to move in a direction of force hence producing electric current

Fig. Conductor

In conductor electrons are free in valence band and can move to the conduction band, hence making a conductor conducts electricity at room temperature

In conductor valence and conduction band overlap each other. Because there is no forbidden energy gap that hinders the flow of electrons from the valence to the conduction band.

Note: Conductors conducts electricity at room temperatures while at high temperature conductors lose their conductivity (conductivity decrease with temperature)

INSULATORS

Insulators: Are material that do not allow electric current to pass (flow) through them.

Hence these materials do not conduct electricity under the influence of an electric field

Examples of insulators glass, paper, Teflon, rubber and most plastics

Insulators do not conduct electricity this is because electrons are not free to move due to high resistivity they have between them

In insulators the valence in valence band cannot manage to move to the conduction band because insulators have wider forbidden energy gap. But at high temperature few electrons can move to the conduction band across the gap and make it conduct electricity but less than that of conductors

Conditions that make insulators conduct some electricity

1. When heated to very higher temperature

2. When large voltage is applied; the electric field force electrons away from it

This is known as the breakdown voltage of an insulator

Fig. Insurator

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SEMICONDUCTORS

Semiconductors: Are materials that their conductivity relay between conductors and insulators

Fig. Semiconductor

In semiconductors electrons are free in valence band and empty in conduction band but cannot move to the conduction band across the forbidden gap, but at a certain high temperature few electrons can manage to move from valence band to the conduction band and make it conduct electricity less than conductor and more than insulators. Because it has a narrow forbidden energy gap

Fig. Difference between conductor, semiconductor and insulator in

terms of their bands

Note: The general name of electrons in the conduction band and holes in the valence band is called free charge carriers

Fermi level: Is the uppermost level reached by electrons in materials

In which at low temperature i.e. 0K the electrons are at the lowest energy level but at high temperature electrons are at uppermost level called Fermi level

Types of Semiconductors

There are two types of semiconductors

1. Intrinsic semiconductors

2. Extrinsic semiconductors

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1. INTRINSIC SEMICONDUCTOR

Is a semiconductor that is pure enough in which the impurities do not affect its electric conductivity. Because it has equal numbers of negative carriers (electrons)

and positive carriers (holes)

Example of extrinsic semiconductor Silicon and Germanium

Note: The electric conductivity of an intrinsic semiconductor increase with temperature because it is a semiconductor

2. EXTRINSIC SEMICONDUCTOR

Is a semiconductor that is impure hence its electric conductivity is increased by adding impurities (dopants)

Dopants: Are materials added to the extrinsic semiconductor to make it conductive by the process called doping

Doping: Is the process of adding impurities (dopants) to an intrinsic semiconductor to improve its conductivity

Mechanism of doping

The mechanism of doping is done into ways namely n-type doping and p-type doping

By N-type Doping

It is done by using impurities material with electrons (negative charges/carriers) to produce the n-type semiconductor (the conductor with majority number of electrons)

Qn Explain how n-type semiconductor is produced

Answer It is produced when extrinsic semiconductor is doped with n-type impurities

Example the element in group four (IV) eg silicon is doped with the element in group five (V) eg antimony (Sb), one electron is left making the majority electrons and minority holes; this is because at normal temperature electrons move to the conduction band but does not results into formation of holes in the valence band

In his doping there is one or extra electron to donate therefore it is called donor atom

Fig. N-type doping

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By P-type doping:

It is done by using dopants with positive charges (holes) in order to produce the holes in the valence band, in this process the P-type semiconductor is produced

Qn: Explain how P-type semiconductor is produced

Answer: It is produced when the extrinsic semiconductor is doped with P-type impurities (dopants)

Example When one atom from group four (IV) such as Silicon is doped with one atom from group three such as Boron one electron in four electron of silicon is missing and can accept one from the other atom to complete the four bond, such dopant is called acceptors. Therefore during acceptance they lose one bond and form a hole making semiconductor to remain neutral

Fig. P-type doping

THE P-N JUNCTION

Is a junction made by combining a P-type and N-type semiconductor in a single continuous crystals

Fig. P-N junction

Mode of action of a P-N junction

After the PN junction is constructed electrons move from the N – Type to the P-Type at the same time holes move from the P-Type to the N-Type to capture the electrons. This movement of electrons and holes causes the N-side to become positive and the P-side to become Negative charged and hence creates a pd across a boundary (junction). This pd creates a barrier of movement of holes and electrons. Hence a region nearly a boundary is fairly free of charge carriers and therefore called depletion layer

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Fig. PN Junction showing depletion layer

QN With the diagram explain how a depletion layer is obtained in a p-n junction

Answer Sees explanation above

Forward Bias of a p-n Junction

The forward bias is a construction (occurs) when the P-Type side of a PN-Junction is connected to a positive terminal of a battery and the N-Type side being on the negative terminal of a battery and allows the flow of current.

During connection the positive charges applied to the P-Type repel the holes while the negative charges applied to the N-type repel the electrons as the process continue they push the charge to the junction and reduces the width of the depletion layer.

Therefore this connection is the one used to reduce the width of the depletion layer

Fig. Forward biasing of a PN Junction

Reverse bias of a PN Junction

The reverse bias occurs when the positive terminal of a battery is connected to the N-Type side and the negative terminal of a battery to the P-Type side of a PN Junction; hence produce a reverse bias effect. In which holes are pulled away by the negative charges in the P-Type and the electrons are pulled away again by the positive charges

In the N-side of the junction making the depletion layer wider apart.Therefore the electric field grow beyond the critical level then the junction break down and produce the voltage called break down voltage

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Diodes

Diode: Is an electric device that allow an electric current to flow easy in one direction

Note: It is a semiconductor diode

Fig. Diode diagram

Fig. Diode symbol

Types of diodes

1. Semiconductor diode

2. Metal semiconductor diode

3. Light-emitting diode

4. Zener diode

1. Semiconductor Diode

It is made by semiconductor materials such as germanium

2. Metal Semiconductor Diode

It is made by depositing a metal on a surface of a semiconductor material

3. Light Emitting Diode

Is a semiconductor diode that emit light when electric current is applied in a forward direction of a diode

4. Zener Diode

It is used to operate in a reverse breakdown voltage called zener voltage

Also it is used as a voltage regulator device

A Rectifier: Is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction

It consists of diodes

Rectification: Is the process of changing alternating current to direct current. Or

Is the process of obtaining DC fro AC

During the process of obtaining DC fro AC also current and Voltages are obtained

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Advantages of using DC from AC

1. The DC is cheapest

2. The DC is easy to use

Types (ways) of Rectification

1. Half wave rectification (HWR)

2. Full wave rectification (FWR)

1. Half wave rectification (HWR)

Is the rectification (the process of changing AC to DC) by using one diode only

It is connected to the step down transformer

Fig. Diagram of Half wave rectification (HWR)

Fig. Graph of half wave rectification

The voltage obtained iv half wave rectification may not be used until it is smoothed by connecting the capacitor parallel to the road resistance in Half wave rectification

Fig. Smoothing process

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2. Full wave rectification (FWR)

Is the process rectification which is achieved by two or more diodes

Fig. Diagram of full wave rectification (FWR)

In forward direction current flows from O through A, D1, RL back to O the at this time the D1 is active (Forward) while D2 is in reverse direction and vice verse. D1 and D2 are in parallel

Fig. Graph of full wave rectification

More diodes connected in Metre Bridge

Fig. Diodes connected forming a Metre Bridge

Here current flow from the source through D4, Load,D3 back to the source as a forward direction and from the source through D2, Load, D1 back to the source at this time D2 and D1 are forward while D4 and D3 are reverse biased making the so called full wave rectification

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Transistor

A transistor: Is a semiconductor diode/device used to amplify and switch electronic signals and electrical power (voltage or current)

It is composed of semiconductor material with at least three terminals for connection to an external circuit.

Note: When a transistor is use as amplifier it amplifies means it rise or increase the signals (voltage or current) of a device

Note: When a transistor is used as a switch it switches OFF or ON an electric current of a device

Uses of transistors

1. It is used as a switch to turn ON or OFF an electric current

2. It is used as amplifier to raise the signals (voltage or current)

3. It is used as oscillator circuit

4. It is used as a regulator circuit

5. It is used in computer to store information or to process data

6. It is used in amplifiers to make the sound signal stronger

Devices (appliances) that uses transistors

Television (TV), Radio, computer, radar, amplifiers

Types of Transistors

There are two types of transistors, which have slight differences in how they are used in a circuit:

1. Bipolar transistor (BT)

2. Field-effect transistor (FET)

1. Field effect transistor (FET)

Field effect transistor: Is a transistor that use (require) only voltage and no current during its operation.

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Therefore for this reason a field effect transistor it require only one charge carrier electron or holes to operate

For a field-effect transistor, the terminals are labelled gate, source, and drain, and a voltage at the gate can control a current between source and drain.

2. Bipolar transistor

Bipolar transistor: Is a transistor that requires a biasing input current (both charge) carries to operate.

Therefore this is an advantage of using bipolar transistor rather a field effect transistor

This transistor has three terminals labelled base, collector, and emitter. A small current at the base terminal (that is, flowing between the base and the emitter) can control or switch a much larger current between the collector and emitter terminals.

Types of bipolar transistors:

1. n-p-n transistors

2. p-n-p transistors

1. PNP Transistor

A p-n-p Transistor is a bipolar transistor made by two pn-Junction diodes joined back to back (reversed) and the n side being between the p sides; hence making the so called Positive-Negative-Positive type of the block, with the arrow which also defines the Emitter terminal pointing inwards in the transistor symbol (Hence pointing in)

A voltage or current applied to one pair of the transistor's terminals changes the current through another pair of terminals. Because the controlled (output) power can be higher than the controlling (input) power, a transistor can amplify a signal

Then, PNP transistors use a small base current and a negative base voltage to control a much more emitter-collector current. In other words for a PNP transistor, the Emitter is more positive with respect to the Base and the Collector

In p-n-p transistor holes are the majority important carriers than electrons

Fig. PNP transistor diagram PNP – Transistor symbol

I_C = I_E - I_B

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PNP-Transistor operation diagram and circuit operation symbol

2. N-P-N transistor

A n-p-n Transistor is a transistor made by two pn-junction diodes joined back to back (reversed) and the p side being between the n sides; hence making the so called Negative-Positive-Negative type of the block, with the arrow which also defines the collector terminal pointing out ward in the transistor symbol (hence not pointing in)

The Collector is connected to the supply voltage V_CC via the load resistor, RL which also acts to limit the maximum current flowing through the device

The Base supply voltage V_B is connected to the Base resistor R_B, which is used to limit the maximum Base current

In a NPN Transistor the majority carriers are electrons through the Base region that makes the transistor action,

These mobile electrons provide the link between the Collector and Emitter circuits

The n-p-n transistor is a current operated device (Beta model) than the p-n-p transistor and that a large current ( Ic ) flows freely through the device between the collector and the emitter terminals when the transistor is switched ON

NPN Transistor diagram NPN transistor symbol

I_E = I_B
+I_C

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NPN Transistor operation diagram (connection) and circuitry symbol

Information Signals

Information is usually transmitted in electric devices in form of signals

Categories of signals

1. Analogue signals

2. Digital signals

1. Analogue signal

An analogue signals: Are electric signals that convey or store information by means of variation in a continuous form

It is the first mode to be investigated in large number while the use of micro electronics has reduced the cost of analogue technique and now makes the digital methods possible

The information is converted from some physical form such as sound, light, temperature, pressure into electric signals by a device called transducer

Transducer: Is a device that converts an input of one form to an output signal of another form

Each unique signal value taken input represents different information (output)

Eg 1Volt = 1˚C, 40V = 40˚C, 12Pa = 12Volts etc

2. Digital signal

These are none continues electric signals; hence they convey information is steps (pulse) or digits of two discrete levels. This means that the value of each pulse is constant and move from one digit to the next

The digital signal are derived from the analogue signals

The main advantage of using digital signals over analogue signals is that “The signal

level or value needed can be approximated within a fixed number of digits or bits and

the whole process of approximating is called quantisation

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Electronic amplifier

Amplifier: Is a circuit used to increase the amplitude of a given input signals. Or

Is an electric device used to increase the strength (power) of a given input signal

Amplification: Is the process of increasing the amplitude (strength or power) of a given input signals

The relationship between the input and output of the amplifier is called transfer function and the magnitude of the transfer function is so called gain

Types of amplifiers

1. Single-Stage Amplifier

2. Multi-stage amplifier

Single-stage amplifier

Single-stage amplifier has only one amplifying device. It consists of amplification stage that includes a transistor. The transistor is connected to a load resistor through which a load current flows. The value of the load resistor together with the transconductance value affects the amplifier’s voltage gain.

Therefore Single-stage amplifiers include

1. Common-emitter (CE) amplifier

2. Common-collector (CC) amplifier

3. Common-base (CB) amplifier

1. Common-emitter amplifier (CEA)

The amplifier is named so (common-emitter amplifier) because both the signal source (input) and the load (output) share the emitter as the common connection point

In the common emitter amplifier, the base terminal of the amplifier saves as input, the collector is the output and the emitter is common to both, that is why is called the common emitter amplifier

Fig. Common-Emitter amplifier circuit

Note: The amplifier is named according to the one among the emitter, collector and base which is common to both and is at the centre of the other

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The emitter-base junction is forward biased by power supply VBB while the collector-base junction is reversed by power supply VCC

The function of capacitor C1 is to provide the d.c. isolation at the input while the capacitor C2 is to provide d.c. isolation to the output of the amplifier

2. Common collector amplifier (CCA)

In this type of amplifier, the base terminal of the amplifier saves as input, the emitter

as output while the collector is common to both

Common-Collector amplifier circuit

The function of capacitor C1 is to provide the d.c. isolation at the input while the capacitor C2 is to provide d.c. isolation to the output of the amplifier

3. Common-base amplifier

In the common base amplifier, the emitter terminal serves as the input; the collector terminal saves as output, while the base terminal is common to both

Fig. Common-Base amplifier circuit

The emitter base junction is forward-biased by the power supply VEE whereas the collector-base junction is reversed by VCC

The input signal is fed to the emitter base circuit while the output signal is taped from the collector-base circuit

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CHAPTER: 6

ELEMENTARY ASTRONOMY

The word Astronomy comes from two Greek words Astron and Nomos

Astron:- Means stars and

Nomos:- Means Laws or culture

Therefore Astronomy means the law of the stars

Astronomy: Is the study of the universe and the heavenly (sky) bodies. Or

Is the branch of science which deals with the study of origin, evolution, composition, distance and the motion of all bodies and scattered matter in the universe

Universe: Is all of the space and everything in it. Or

Is the totality of space and time together with matter and energy

Astronomers are the people who deal with astronomy

The Importance of Astronomy in Everyday Life

1. It was the earliest method of measuring time

That:

(i) A day was the duration of sunrise and sunset

(ii) The month was derived from the phases of the moon

(iii) The year was derived from the changing position of sunrise

2. It was used to develop calendars that made it possible to predict the seasons.

Such as agricultural activities; to dictate the time for planting and harvesting

3. It is used by land and sea navigators to determine position by using the sun during day time and stars at night

4. Helps us to understand the earth and the life it supports, originated from and how it evolved.

5. It Presents a new frontier (settlement) for exploration (researchers)

6. Helps us to discover satellites (natural and made) used for weather forecasting (predict/estimate) and telecommunication

Solar System

The solar system: Is the arrangements of the planets and solid objects in space in relation to their position from the sun. Or

Is the name given to the collection of heavenly bodies that revolve around the sun

Note: The solar system is made up of the sun and the celestial (sky/earthly) objects bound to it by gravity.

The celestial objects include the eight planets and their known moons and billions of small bodies that include Asteroids, Comets, Meteoroids (Meteorites), Stars and interplanetary dust.

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Stars and planets

A star : Is a large celestial body made up of hot gases known as plasma

Plasma: Is an ionized gas in which a certain proportion of electrons are free rather than bound to an atom or molecule

Note: Stars radiate (send) energy derived from the thermonuclear reactions in the interior region

Thermonuclear reactions: The reaction that require heat to take place

The sun is a large star and closest to the earth at an average distance of 149.6 millions Km. This distance is called Astronomical unit

1 Astronomical unit: (1AU): Is the mean distance from the earth to the sun which is equal to 1.5x10⁸Km. Or

Is the distance between the earth and the sun which is used to measure distances across the solar system

Light year: Is the distance travelled by light in one year which is equal to 9.46x10¹²Km

The sun: Is the star; it is the same as other millions of the stars we see in the sky but.

Note: The sun looks much bigger and hotter than the rest of the stars because:-

It is relatively nearer to the earth and bigger than other

The sun is a member of solar system but is a unique and it produces its own light while all other members do not. The other members are being seen because they reflect light from the sun to us. For example the moon shine because of the light received from the sun which is reflected to us. Without the sun the moon would be dark and not be visible

The sun gives out light and heat because of its very high temperature about 6000˚C at the surface and 14, 000, 000˚C in the interior which is hotter

QN: Without the sun no life is would be possible on the earth: This is because all energies on earth comes from the sun

A Galaxy: Is a giant collection of stars, gas and dust.

Most stars in the universe are in the galaxies. Nearly all of the stars visible in the night sky are within our own galaxy, sometimes called the Milky (cross) Way Galaxy

Other larger galaxy is the Andromeda galaxy

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Galaxies are classified on the basic of their shape as

(i) Spiral galaxy

(ii) Elliptical (round) galaxy

(iii) Irregular (not really) galaxy: the one with unknown features (shape)

Planet: Is a major (large) object which is in orbit around a star

There are eight planets which are Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune.

Characteristics of a planet (For a body to be a star should be)

(i) Should be a celestial/sky body that orbits a star

(ii) Should be massive/larger enough so that its own gravity cause it to assume a spherical shape

(iii) Should be cleared the neighbourhood around its orbit

Pluto is not considered as a planet because it resides/live in an area of space populated by numerous other objects. It is now designated a dwarf planet. The dwarf planet does not meet the third characteristic i.e has not cleared the neighbourhood around its orbit

Differences between stars and planets

	Stars	Planets
	Emit their own light	They reflect light from the sun
	Twinkle at night	Do not twinkle at night
	Appear to be moving from east to west	Planets move around the sun from west to east
	Have very high temperature of (6000˚C)	Their temperature depends on their distances from the sun
	Countless in number	There are eight in the solar system
6.	Very big in size but appear small because they are very far away	Very small in size as compared to stars

Types of planets

1. The Inner (Terrestrial/earth) planets

2. The outer (Jovian) planets

1. The Inner (Terrestrial/earth) planets

They are called terrestrial planets because their structure is similar to the earth

Are the first 4 planets in the solar system which includes Mercury, Venus, Earth and Mars

Common features of Inner (terrestrial) planets

(i) They have a core of molten metals

(ii) They have thin atmosphere

(iii) They have few natural satellites or moon or no satellites

(iv) They have mantle reach rich in iron and magnesium

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2. The outer (Jovian) planets

Are the last 4 planets in the solar system which includes Jupiter, Saturn, Uranus and Neptune

Common features of outer (Jovian) planets

(i) They are made up of gases (except Pluto which is made up of ice and rocks)

(ii) They have ring system surrounded them

(iii) They have larger number of satellite or moon

(iv) They are the furthest from the sun

The planet Venus

It shines brightly like a very bright star in the sky but does not do so for a long time before it disappears from the sky because it lies between the sun and the earth.

When Venus is east of the Sun it sets after the sun sets hence is called an Evening Star. But when it is west of the sun it sets in the earth but it rise before the sun so it is called Morning Star

The planet Jupiter

It is the first largest planet in the solar system; hence it is one of the conspicuous in the sky this means that

During a cloudless night it appear as a very larger Bright Star

The planet Saturn

It is the second largest planet in the solar system after Jupiter

The planet has ten (10) satellites but the innermost one i.e. the tenth broke into fragments due to the strong gravity of the planet; these fragments formed the ring system around the planet

(A) Asteroids (minor planets)

Is the collection of particles found in the region between Jupiter and Mars that revolve around the sun as the planet do

Note: Asteroids are mass of stones of different sizes; the particles that form asteroids in the sky cannot be seen directly even with a powerful telescope but by using the so called Zodiacal light

Zodiacal light: Is the bright haze (mist, fog) seen in the sky after sunset and before sunrise due to reflection of light from the sun

Note: Asteroids are small solar system bodies in orbit around the sun, especially in the inner solar system. Asteroids are smaller than planets but larger than a speck of dust

(B) A comet: Is a solid body orbiting the sun typically composed of rock dust or ice.

It is a glowing asteroid in space which can be seen with naked eyes

Most comets were formed from condensed interstellar (space) gas and dust clouds in the early stages of the creation of the universe

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These are asteroids that happen to enter the earth’s atmosphere.

When heat is increased near it, it burns out in a short time hence the asteroid ash or dust falls to the earth’s surface

(D) Meteorites: Are asteroids that are not burnt up completely and manage to reach the earth.

They fall to the earth with so much force that they make huge craters.

There are two known meteorite sites in Tanzania these include

· In Mbozi district in Mbeya region

· In Malampaka Shinyanga

The other are

· Barringer crater in Arizona state in USA (200M wide)

· Vredefort ring crater in Transvaal South Africa (400Km wide the 1^st in the world)

Constellations

Constellation: Is a group of stars that form a definite shape or pattern when viewed from the earth. Or

Is the group of stars that appear in the form of closed groups forming a recognized shapes and pattern

Constellations are usually seen and named after mythological/science characters, people, animals and things. There are about 88 known constellations. The various constellations are visible during a particular period of the year.

Examples of constellations

1. Leo → the lion

2. Orion → the hunter

3. Canis major → The great dog

4. Ursa major → The great bear

5. Gemini → Boy and girl

6. Scorpios → Scorpion

Uses of constellation in everyday life

1. Agricultural.- Before there were proper calendars, people had no way of

determining when to sow or harvest except by the stars. Constellations made the patterns of the stars easy to remember

For example: The ancient (passed/long) people knew that when the Orion started to be fully visible winter was coming soon hence allowed farmers to plane ahead

2. Navigation. Navigators used these constellations to know the direction when

travelling across the globe by using ships and by determining the latitudes (North or South) using the constellation Ursa major (great bear)

· It allowed for the discovery of America

· The spread of European culture

· Civilization (good)

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3. Religious -In early days, people thought that the gods lived in the heavens and that

the gods created the constellations. Many cultures believed that the position of the stars were their god’s way of telling stories.

But indeed the Greeks named the constellations after their mythological heroes (giants)) and legends (stories)

For example: Orion was a great hunter – he was the son of Neptune (god of the sea)

Force of Gravity (gravitational force) which maintains Celestial Bodies in their Orbits

Gravitation force: It the attractive force exists between any two objects that have mass. It pulls objects together and acts on all matter on the universe, hence it is sometimes referred to as universal gravitation because it acts on all matter in the universe from the smallest atom to the largest stars

Newton’s law of universal gravitation

It states that: ‘Every single point mass attracts every other point by a force directed along the line joining the two masses.' Or

All bodies in the universe attracts each other with a force that is directly proportional to the product of their masses and inversely to the square of their distance apart

The force is proportional to the product of the two masses and inversely proportional to the square of the distance between the point masses.

Where:

F Is the magnitude of the attractive force between the two point masses.

G Is the universal gravitation constant.

M₁ Is the mass of the first point mass.

M₂ Is the mass of the second point mass.

r Is the distance between the centres of the two point masses.

Note: Natural satellites (moons) orbits planets while artificial satellites orbit the earth in the same way as the moon orbits the planets

Example 1: The masses of two bodies at a point source are 420Kg and 870Kg respectively. If are at a distance of 400Km between them calculate the force that hold them apart. If gravitational constant is 10N/kg

Given: M1 = 420Kg, M2 = 870Kg, d(r) = 400km, g = 10N/kg

From

F = 22.8N

The force that holds them (F) = 22.8N

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Gravity: Is the gravitational force that occurs between the earth and the other objects

It pulls the objects towards the centre of the earth

It holds us on the ground and causes objects to fall back to the ground after being thrown in the air

The earth gravitational pull extends out into space in all directions

The further you move away from the centre of the earth, the weaker the force becomes.

The measure of the force of gravity on an object on the earth’s surface is the weight of that object and is measured in Newton (N)

The weight of an object changes depending on its location in the universe.

Gravity = Weight = Mass x Gravitational force

G = W = Mg

The Earth and its Moon

The Surface Features and Temperature of the Moon

The moon of the earth is the sixth largest in the solar system

It has a diameter of 3,476km and a mass of 7.35 x 10²²kg. Like the earth, the moon has an iron core surrounded by a rocky mantle and crust

Unlike the earth, no part of the moon’s iron core is molten so it does not have a magnetic field. Surface gravity on the moon is 1/6 that of the earth

The moon revolves in a anticlockwise direction around the earth in an elliptical orbit The moon’s orbit is tilted at 5° relative to the earth’s orbit around the sun

The distance between the earth and the moon varies from perigee (nearest the earth) where it is 356,000km to apogee (furthest from the earth) where it is 406,000km

The average distance is 384,000km.

It takes the moon 27.3 earth days to complete one orbit, a period called the Sidereal (season) month The moon also rotates about its axis, The side which faces the earth is called the near side while the side which faces away is called the far side

The spinning of the earth causes the moon to rise and set each day, just like the sun Because of moons’ orbital motion around the earth, it (the moon) rises about 50 minutes later each day. As a result, the moon can be seen at different times of the day and night during a month

The temperatures on the surface of the moon are on average 107°C during the day and 53°C during the night

Surface features of the moon

There are two primary types of features (terrain) on the moon. These are

· Heavily cratered very old lunar highlands (bright area)

· Relatively smooth and younger Maria (dark area)

The bright areas are the lunar highlands that have many craters and covered with a highly reflective layer of fine dust. The highlands are geologically the oldest parts of the moon’s surface

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The dark areas are low areas similar to ocean basins on the earth. They are with dark solidified lava and are less cratered than the highlands

Galileo called these areas maria (matia), Italian word for seas, because their dark smooth surface appears to be large bodies of water

The maria which makes 16% of the moon’s surface, are huge impact craters that were later flooded with molten lava. Most of the maria is covered with regolith, a mixture of fine dust and rocky debris produced by meteor impact

Ocean Tides: Are tides that occurs in oceans

Tide(s): Is a periodic rise and fall of larger masses of water

The Causes of Ocean Tides

Tides are caused by the gravitational interaction between the earth and the moon

Note: the earth and the moon are attracted each other like magnets of different poles

The moon tries to pull at anything on the earth to bring it closer. But the earth is able to hold onto everything except the water. This is because water always moving, the earth can't hold onto it and the moon is able to pull at it. This results into ocean tides

Each day, there are two high and two low tides. The ocean constantly moves from high tide to low tide, and then back to high tide. There is a time interval of about 12 hours and 25 minutes between the two high tides.

How tides occur

This occurs when gravitational attraction of the moon causes the oceans to bulge/rise out in the direction of the moon. Another bulge occurs on the opposite side since the earth is also being pulled towards the moon and away from the water on the far side

As the sun, moon and earth interact ocean level fluctuate (stress), as the moon travels around the earth, and as they together travel around the sun, the combined gravitational forces cause the world ocean water levels to rise and fall

Types of tides

1. Spring (strong) tides

2. Neap (weak) tides

1. Spring tides

This occur during the full moon, the new moon, the sun and the earth are in a line

At this time the high tides are very high causing the spring (strong tides) and the low tides are very low causing the neap (weak) tides

Note: the gravitational force of the moon and the sun both contributes to this tides

Proxigen spring tide: Is a rare unusually high tide that occurs at most once every 1.5 years

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2. Neap tide

These occurs when the sun and the moon are not aligned, the gravitational forces cancel each other out, and the tides are not very high or very low

REVIEW QUESTIONS ON CHAPTER: 6

1. (a) (i) What is astronomy

(ii) Explain the importance of astronomy to mankind

(b) Define (i) Solar system (ii) Planets

2. (a) (i) State three characteristics for a heavenly body to be termed as a planet

(ii) Give two types of planets and at least two examples for each type

(b) What is the meaning of the following terms

(i) Miner planets (ii) shooting star (iii) Zodiacal light

3. (a) Explain the force that keeps the earth in its position

(b) (i) What is constellation. List down at least three known constellations

(ii) Give at least three uses of constellations

4. (a) (i) What is asteroid

(ii) Distinguish between a comet and a meteor

(b) (i) Name the planets which are closest to the sun, and furthest from the sun

(ii) Name two objects in space which are the earth’s nearest neighbours

the following names

(i) An evening star (ii) Morning star (iii) A shooting star

5. (a) (i) State the Newton’s law of universal gravitation

(ii) What is gravity?

(b) (i) differentiate between perigee and an apogee

(ii) list the surface features of the moon

(i) Rotational motion of the earth about axis

(ii) Revolution of the earth around the sun. (1 year = 365days)

6. (a) (i) Explain what a tide is

(ii) Explain how tides occurs

(b) Explain with diagram how two types of tides occurs

7. (a) (i) Explain why the sun looks much bigger and hotter than the rest of stars

(ii) Name the heavenly bodies that are heavenly closest to the sun

(b) (i) Give only three known galaxies

(ii) Name the galaxy in which the solar system is a part

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8. (a) (i) Name the largest planet in the solar system

(ii) Name two brightness planets in the solar system

(b) A satellite has a radius (R) of 42000Km. Find its speed if it can complete

one orbit in 24 days

9. (a) (i) Define stars (b) Meteoroid

(b) Mercury planet is 58x106km from the sun and it takes 88 days to complete one orbit around the sun. Calculate its speed in km/h

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CHAPTER: 7

GEOPHYSICS

Geophysics: Is a branch of science that deals with the physical, chemical, geological, astronomical and other characteristic properties of the earth.

Is the branch of science that deals with characteristic properties of the earth which includes physical, chemical, geological and astronomical

It deals with geological phenomena such as the temperature distribution of the earth’s interior, the source, configuration and the geomagnetic field.

Interior Structure and Composition of the Earth

The structure of the earth is composed of three major zones arranged in concentric manner. These are crust, mantle and core.

1. THE CRUST

Is the outer solid layer o the earth. It is thin (5 to 15km) compared to the radius of the earth (6,371km)

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Types of crust

Continental crust and Oceanic crust

· Continental crust: It is heterogeneous and of low density (2 to 2.8 tonnes per cubic meter)

It is composed mainly of granites and sedimentary rocks

· Oceanic crust: This is basaltic and more denser (3.0 to 3.1 tonnes per cubic meter)

Both the continental and the oceanic crusts floats on the denser mantle

Because of its low density, the continental crust floats on the mantle at a higher elevation, forming the land masses and mountains

The continental crust is 30 to 70 km thick. The denser oceanic crust floats at a lower elevation forming oceanic basins. It is about 8km thick

The boundary between the crust and the mantle is called Mohorovicic discontinuity or simply Moho

2. THE MANTLE

It begins from the Moho and extends to a depth of 2,900km below the earth’s surface, up to its boundary with the earth’s core

The layer (boundary) between the mantle and core that separate them is called the Gutenberg discontinuity

The mantle contains about 70% of the earth’s mass. It is composed of rocks (in plastic state), both in solid and molten states.

Note: The rocks forming the mantle are said to be in plastic state because it is in both solid and molten states

The upper surface of the mantle has the temperature of about 870°C, and this temperature increases downwards through the mantle to about 2,200°C near the core

Function of the mantle

1. It is the main mechanism of heat transfer from the core to the crust which is in circulation of materials

2. It is the main force that drives the movement of Continents, Volcanism and Earthquakes

3. THE CORE

Is the innermost part of the earth that extends from the Gutenberg discontinuity to the earth’s geometric centre

The core is made (consists) of two distinct regions namely

The inner core and the outer core

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· The inner core: It is composed of solid material (iron-nickel alloys) because of the high pressure at this depth cools the magma formed

· The outer core: Is composed of liquid of molten nickel and iron known as magma It extends from the mantle to a depth of about 5,000km below the earth’s surface

QN: Explain why the outer core is liquid while it is in low temperature and the inner core is solid while it is in high temperature?

Answer: This is because in the inner core there is strong tremendous/high pressure that crowds/assemble the atoms tightly together and prevents the liquid state

QN: Describe the composition of the layers of the earth

Answer: The Composition of the Layers of the Earth

Continental crust is made of granite and sedimentary rocks forming the lands and the mountains while the oceanic crust forms oceanic basins. Mantle is made of solids and molten rocks. The outer core is made of molten nickel and iron called magma while the inner core is solid because of the high pressure. The crust and the mantle are separated by the mohorovicic discontinuity.

The Importance of the Layers of the Earth

1. Continental crust forms the land and mountains of the earth on which all human activities are carried out e.g farming, housing etc

2. Oceanic crust forms the base of the oceans and seas on which oceanic water rests and all aquatic organisms like fishes lives

3. The mantle provides the heat transfer from the core to the outer layers a process which causes the volcanic actions and earthquakes

TECTONIC PLATES (Lithospheric plates)

Tectonic plates: Are pieces of cracked earth’s crust and part of the mantle (uppermost mantle) that are collected together

These plates floats with a very slow speed on top of semi-molten rocks

The movement of tectonic plates i.e. some continents are moving apart and towards each other; this process of moving is called continental drift

The line where two tectonic plates meet is called boundary

Types of boundaries

A. Destructive/destroy (convergent) boundary

B. Constructive/opposite (divergent) boundary

C. Conservative (transform/change) boundary

A. Destructive (convergent) boundary

Is one that found at the edges of two plates moving towards each other (meet head one)

The impacts of the two colliding plates buckles (cut) the edge of one or both plates up into a rugged (round) mountain range; and sometimes bends the other down into a deep sea flow trench.

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If one of the collided plates is tapped with oceanic crust; it is forced down into the mantle, melted and hence magma rises and solidify into new crust

Note: When the crust is destroyed and recycled back into the interior of the earth this process is called subduction zones

Types of destructive boundary

1) Oceanic – Oceanic boundary

2) Oceanic – Continental boundary

3) Continental – Continental boundary

1) Oceanic – Oceanic boundary

It is when two oceanic plates meet head on and is usually subducted under the other forming a deep oceanic trench; resulting under sea volcanoes

2) Oceanic – Continental boundary

This occurs when an oceanic plate pushes into and subducts under a continental plate, the overriding continental plate is lifted up and a mountain range is created

3) Continental – Continental boundary

This occurs when two continents meet head on, neither is subducted because the continental rocks are relatively light and crust tends to be pushed upward or sideway

B. Constructive/opposite (divergent) boundary

Is a one formed at the edge of two plates moving away (opposite) from each other

It occurs when two tectonic plates are moving oppositely from each other

EFFECTS

(i) A new crust is created as two or more plates pull away from each other

(ii) Oceans are created and grow wider when plates pull apart

(iii) As mass of land Brock the surrounding water fill the space between them

C. Constructive (transform/change) boundary

It is formed when two plates slide past each other without moving apart or towards each other.

Neither is added at the boundary nor destroyed

Volcanoes and Earthquake

The two terms are closely related, they are caused by the movement of molten rock and heat deep inside the earth. These movements are referred to as subterranean (underground) movements. Most earthquakes and volcanic activity happen near tectonic boundaries (plates).

Volcanoes

Are places where molten rocks (magma) leaks out through a hole or crack in the earth’s crust

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The Origin (Occurrence) of Volcanoes

Volcanoes are places where molten rock called magma leaks out through a hole or a crack in the earth’s crust

Magma originates from the mantle, where high temperature and pressure cause the rock to melt. When a large pool of magma if formed, it rises through the denser rock layer towards the earth’s surface

Magma that has reached the earth’s surface is called lava. Most volcanoes form along constructive and destructive boundaries between tectonic plates while few volcanoes form far away tectonic plate boundaries i.e. form at the mantle that are hotter than normal. Eg. Nyamulagira Congo

Types of volcanoes

Fissure volcanoes and central volcanoes

1. Fissure volcanoes: These occur along the cracks in and between tectonic plates and can be many kilometres long.

Lava is usually ejected quietly and continuously, forming enormous plains or plateaus of basaltic volcanic rock.

2. Central volcanoes: These have a single vertical main vent through which magma

reaches the earth’s surface.

They usually develop a cone shape that builds up from successive layers of lava and ash

Classification of volcanoes

Volcanoes are classified into three categories based on their frequency of eruption, namely: Active volcanoes, Dormant volcanoes and Extinct volcanoes

1. Active volcanoes: Are those that either erupt constantly or have erupted in recent times. Eg: Oldonyo Lengai

2. Dormant volcanoes: Are those that have been inactive for some times (a few thousand years) but can erupt again. Eg; Mt Kilimanjaro

3. Extinct volcanoes: They have not erupted in recorded history, and will probably never erupt again

Effects of Volcanoes

Positive (advantage) Effects

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1. Provide resource of energy extraction (geothermal source) due to conversion of heat from earth’s crust which is very clean and inexhaustible

2. Minerals: Volcanic eruptions bring valuable minerals (which are important economic resources) to the earth’s surface

3. Fertile soil: When volcano erupt it throw out a lot of ash layers that contains useful minerals that are converted to fertile soil

Soil: Volcanoes help in soil formation by bringing important minerals from deep underground onto the earth’s surface.

4. Tourism: volcanoes attracts many guests from different areas visiting the area such as Warm bathing lakes, Hot springs, Bubbling mud pools and stream vents contributing in shops, restaurants, hotels

5. Landscape: Most of the earth’s surface is covered with volcanic rocks; Volcanoes are also responsible for the formation of many mountains and islands

Negative (disadvantage) Effects

6. Vegetation and wildlife: Volcanic eruption sometimes set the surrounding vegetation into fire. Wild animals are also killed by being buried into the lava or being burnt by the forest fires

7. Environment: Volcanic eruptions emit harmful gases into the environment that contribute to global warming and climate change eg. Sulphur dioxide

8. Human life and property: Volcanic eruptions sometimes kill people and destroy property.

9. Sea: during volcanic eruption earthquake happen and tsunamis may be created and destroy the sea

Earthquake

An earthquake Is a sudden movement or vibrations in the earth’s crust

Is the vibration of the earth’s crust when the earth experiences a stress

Is a sudden motion or shaking of the earth caused by a sudden release of energy that has accumulated within or along the edges of the earth’s tectonic plates

An earthquakes happen when rocks in the earth’s crust move suddenly, shaking the earth. Earthquake also occurs as a result of movement of magma at constructive boundaries under volcanoes and where continental plates collide and push mountain ranges.

How earthquake occur

Mostly occur on or near the boundaries between tectonic plates also occur far from plate boundaries

Such earthquakes probably occur as a result of faults formed millions of years ago

Hypocenter or the focus of the earthquake: Is the point within the earth where an earthquake begins

Earthquake rarely occur along constructive plate boundaries.

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TSUNAMI: Is a sea waves caused by the disturbance of the ocean floor either by earthquake or a volcanic activities

Seismic waves

Are the energy waves released by an earthquake

They are grouped into three categories:

Ø Primary waves or p-waves: Are the first waves released from the hypocenter. They are felt as a sudden jolt.

Ø Secondary waves or s-waves: These arrive a few seconds later after p-waves

They are felt as a series of side-to-side tremors

Ø Surface waves.-They radiate outward from the point (epicentre) on the earth’s surface directly above the hypocentre.

Epicentre: Is the point on the earth’s surface directly above the hypocentre (focus)

There are two types of surface waves:

1. Rayleigh waves (ground roll): create a rolling movement that makes the land surface move up and down

2. Love waves: Make the ground shift from side to side. Moves horizontally

It is the surface waves that damage to surface structure such as buildings and hydroelectric power plants.

Earthquake scale (Principle of measurement)

The nature of an earthquake is usually described by measuring two properties, namely the magnitude and intensity

The magnitude of an earthquake Is a measure of the energy it releases, usually measured on the Richter scale

The Richter scale: This is an instrument (device) using scales to record (measure) the magnitude of the earthquakes basing on their amplitude of the largest seismic waves

The intensity of an earthquake: Is a measure of its strength based on the changes it causes to the landscape, usually measured on the Modified Mercalli scale, calibrated from 1 to 12.

Note: An earthquake can have only one magnitude. However its intensity reduces as the seismic waves spread out from the hypocentre, just the same way the loudness of a sound changes as you move away from the source

The Seismograph: Is an instrument used to record ground movements caused by earthquakes

Earthquakes hazards

The following are some of the hazards associated with earthquakes:

1) Landslides

2) Tsunamis

3) Collapsing buildings

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4) Fire outbreak

5) Backward rivers

Earthquake warning signs

The following are important signs that are observed before an earthquake occurs:

1) Thermal indicator

2) Water indicator

3) Seismo electromagnetic indicator

4) Animal indicator

5) Human indicator

Precautions to be taken during an earthquake

The following are some precautions that can be taken to minimise injuries or death of human beings in the event of an earthquake:

1. If you are indoors during an earthquake, drop, cover and hold on. Get under a desk, table or a bench. Hold on to one of the legs and cover your eyes. If there is no desk or table nearby, sit down against an interior wall

2. Pick a safe place where things will not fall on you-away from windows or tall heavy furniture.

3. Do not run outside when the earthquake happens because bricks, roofing and other materials may fall from buildings during and immediately after an earthquake, injuring persons near the building

4. Wait in your safe place until the shaking stops, then check to see if you are hurt

Note: You will be better able to help others if you take care of yourself first, then check on the people around you

5. Move carefully and watch out for things that have fallen or broken creating hazards. Be ready for additional earthquakes called aftershocks

6. Be on the lookout for fires. Fire is the most common earthquake-related hazard due to damaged gas and electrical lines

7. If you must leave a building after the shaking stops, use the stairs and not elevator

8. If you are outside during an earthquake, stay outside. Move away from buildings, trees, streetlights and power lines. Crouch down and cover your head.

Structure and Composition of the Atmosphere

The Vertical Structure of the

The atmosphere: Is a layer of gases containing numerous small suspended solid and liquid particles surrounding the earth.

The atmosphere is divided into regions based on its thermal characteristics (temperature changes), chemical composition, movement and density. It is divided into five regions, which are:

1. Troposphere

2. Stratosphere

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3. Mesosphere

4. Thermosphere

5. Exosphere

The Composition of the Atmosphere

Describe the composition of the atmosphere

1. Troposphere

This is the region nearest to the earth’s surface which extends to an altitude up to 10 km above the poles and 20km above the equator. It is the densest part of the atmosphere (80% by mass of the atmosphere) which contains most of the atmosphere's water vapour.

Activities (importance) on the region

a) The temperature in this region decreases with altitude at an average rate of 6°C/km

b) It encourages the change of weather (most of weather phenomenon occur in the troposphere).

c) Clouds and rain are formed within this region

d) Controls the climate and ultimately determines the quality of life on the earth

e) Contain gasses for all living things animals and plants

The boundary which separates the troposphere from the stratosphere is called the tropopause.

At the tropopause, the temperature stops decreasing with altitude and becomes constant. The tropopause has an average height of about 10km

2. Stratosphere

It starts from the tropopause and extends to 50km high. It is more stable, drier and less dense compared to troposphere.

The temperature slowly increases with altitude due to the presence of ozone layer (O₃) which absorbs ultraviolet rays from the sun.

Note: The ozone layer lies in the middle of the stratosphere between 20 and 30km

The Stratosphere together with troposphere is collectively known as the lower atmosphere. The boundary which separates the stratosphere from the outer layer is called the stratopause

Advantages of stratosphere (Activities)

(i) It absorbs the ultraviolet radiations which would otherwise reach the earth’s surface which is harmful to both plants and animals.

(ii) It prevents large storms from extending much beyond the troposphere due to its stability.

(iii) Planes also fly within this layer because it has strong steady horizontal winds which are above the stormy weather of the troposphere.

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3. Mesosphere

It starts just above the stratosphere and extends to 85km high. The temperature at this layer decreases with altitude.

Activities (importance) on the region

Is the layer where most meteors burn while entering the earth’s atmosphere

The boundary which separates the mesosphere from the thermosphere is called the mesopause

4. Thermosphere (the upper atmosphere)

It is just above the mesopause and extends up to 690km high

The temperature increases with altitude due to the sun’s heat

The temperature in this region can go as high as1727°C and chemical reactions occur faster in this region than on the earth’s surface

Contains high concentration of charged particles called ions and free electrons

Activities (importance) on the ionosphere

Ionosphere: Is a part that contains high concentration of charged particles called ions and free ions

1. The larger number of free electrons in the ionosphere allows the propagation of electromagnetic waves

2. Absorbs dangerous radiations such as hard and soft X – rays, extreme ultraviolet radiations

3. It is important in communication over long distance i.e radio waves

5. Exosphere

Is the outermost region of the atmosphere

The upper part of the exosphere is called magnetosphere

Activities (importance) on the exosphere

(i) Has low atmospheric gas pressure such that light atoms such as hydrogen and helium may acquire sufficient energy to escape the earth’s gravitational pull

(ii) The motion of ions in this region is strongly under presence of the earth’s magnetic field

(iii) This is the region where satellites orbit the earth

Global warming: Is the increase of the average temperatures near or on the surface of the earth as a result of greenhouse effect

The effect is caused by greenhouse gases

Greenhouse effect: Is the process in which the emission of radiation by the atmosphere warms the earth’s surface

When heat from the sun reaches the earth’s surface in form of sunlight, some of it is absorbed by the earth. The rest is radiated back to the atmosphere at a longer

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wavelength than the incoming sunlight. Some of these longer wavelengths are absorbed by greenhouse gases in the atmosphere before they are lost to space. During on turn warms the atmosphere. The greenhouse gases act like a mirror, reflecting back to the earth some of the heat energy which would otherwise be lost to space.

Sources of Greenhouse Effect

The sources of greenhouse effect is the greenhouse gases namely

1. Carbon dioxide gas contributes over 50%. Hence it is the main source

It is derived by cleaning and burning of vegetation and fossil fuels

2. Methane (CH₄) it is derived by agricultural activities, burning of vegetation and mining of coal and oil

3. Dinitrogen oxide: (N₂O) from combustion of fossil fuels, use of nitrogen fertilizer, burning of vegetation and animal waste

4. Chlorofluorocarbons (CFCs): Are organic compounds made from Cl, F and C

Derived by fridges, air conditioners and aerosols

The Occurrence of Global Warming

Global warming is primarily a problem of too much carbon dioxide (CO₂) in the atmosphere which acts as a blanket, trapping heat and warming the planet. As we burn fossil fuels like coal, oil and natural gas for energy or cut down and burn forests to create pastures and plantations, carbon accumulates and overloads our atmosphere.

The Consequences (Effects) of Global Warming

(i) Increase in the temperature of the oceans causing the loss of pigments and microscopic of plant cells from coral tissues

(ii) Rise in sea levels: due to thermal expansion of oceans and the melting of land ice causing flooding of coastal land

(iii) Change in world’s climatic pattern: Hence harder to forecast the weather and rain fall unexpected leading to flooding or draught.

(iv) Acidification of the oceans: when oceans sock much CO₂ from living things that dissolve in water.

(v) Extreme weather events: this includes floods, drought, heat waves etc

(vi) Higher or lower agricultural yields.

(vii) Melting of Arctic ice and snow-caps. This cause landslides, flash floods and glacial lake overflow.

(viii) Extinction of some animal and plant species.

(ix) Increase in the range of disease vectors, that is, organisms that transmit diseases.

Solution to global warming

(i) Put in place energy conservation measures to reduce the use of fossil fuels

(ii) Use of cleaner alternative sources of energy such as wind and solar

(iii) Check deforestation and replant trees that would absorb CO₂

(iv) Countries should commit themselves to minimize the emission of green house gases into the atmosphere

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