Mr Ng Han Guan Form 5 Chapter 1: Wave Date:
Guru Cemerlang Physics MSAB
CHAPTER 1: WAVE
1.1 UNDERSTANDING WAVES
1. A wave is a kind of vibration or oscillation that allows energy transfer from one point to
another without transferring matter.
2. Waves can be produced by a system that vibrates or oscillates.
3. Examples of waves:
Light waves Sound waves Water waves
4. Propagation (travelling) of wave is the transfers of energy and the momentum from the source
of the wave to the surroundings.
As the sound waves come out of the speaker, we can see
that the flame flutters.
This shows that energy of the sound waves can be
transferred from the speaker to the candle.
1.1.1 Wavefront
1. A wavefront is an imaginary line or surface that connects all vibrating particles that are in the
same phase (in phase).
2. Points in a wave are in phase if they vibrate in the same direction with the same
displacement.
3. Particles in the same wavefront have the same speed and are at equal distances from their
source.
4. There are two types of wavefront:
Circular wavefronts
Plane wavefronts.
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1.1.2 Types of waves
There are 2 types of waves: Transverse wave Longitudinal wave
1. Transverse wave
The direction of propagation of wave is perpendicular to the direction of vibration of particles.
The wavelength, is the distance between two successive crests or troughs.
AA
A = crests
B = troughs
BB
Example of transverse wave:
i. Water wave ii. Light wave iii. Electromagnetic wave
2. Longitudinal waves
The direction of propagation of wave is parallel to the direction of vibration of particles.
The wavelength, is the distance between two successive compressions or rarefactions.
PP
P = compressions
Q = rarefactions
QQ
Example of longitudinal wave: Sound wave
1.1.3 Properties of a Waves Motion
Properties Definition
Equilibrium position The position of the object where is no resultant force acts on the object
Amplitude, A The maximum displacement from its equilibrium position
Crest (or Peak) The highest point reached by a vibrating particle in a transverse wave.
Trough The lowest point reached by a vibrating particle in a transverse wave.
Period, T The time taken by one oscillation (one complete oscillation or wave). The S.I.
unit is second (s). T = 1/f
Frequency, f The number of complete oscillations produced in one second. The S.I. unit
is Hertz (Hz). f = 1/T
The distance moved by a wave in one second. The SI unit of velocity is metre
Wave speed, v per second (m s-1). v = f = f = 1
T T
In Phase When the particles of wave are moving in the same direction with the same
speed and have the same displacement from the rest position.
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1.1.4 Graph for a Wave
0 0
Displacement – time graph Displacement – distance graph
1.1.5 Damping
1. In an ideal condition, there is no energy gained or loss in an oscillation system.
2. But in a real situation, there is some loss of energy due to friction, air resistance or other non-
conservative force. As the energy of a system decreases, its oscillation decreases as well.
3. Damping is a process where the amplitude of an oscillating system decreases slowly until the
system stops oscillating.
4. Damping is usually caused by (type):
i. External damping loss of energy due to overcome external frictional forces such as air
resistance.
ii. Internal damping loss of energy due to the extension and compression of the
molecules in the system.
Only amplitude, and energy of the system decrease but frequency, does not change.
1.1.6 Resonance
1. The external force supplies energy to the system to enable an oscillating system to go on
continuously Forced Oscillation
2. The frequency of a system that oscillates freely without the action of an external force is
called the natural frequency.
3. A resonance is the phenomenon when the oscilating system is driven (force) to oscillate at
its natural frequency by an external force.
System oscillates at its maximum amplitude.
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Mr Ng Han Guan Form 5 Chapter 1: Wave
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Experiment to show a phenomenon of resonance Barton’s pendulum
1. The natural frequency of a simple pendulum depends on its length.
2. When pendulum X is set into oscillation, its energy is transferred through a thread to another
pendulum. Other pendulums are forced to swing at the same frequency as X.
3. But pendulum X and D have the same length, so there have same natural frequency. So
pendulum D will oscillates with maximum amplitude.
4. The effects of resonance:
i. Constructive (useful)
Electrical resonance: The reception of radio programmes from a distant transmitting
station.
Molecular resonance: The cooking of food using the microwave oven.
Mechanical resonance: The production of sound in many musical instruments.
ii. Destructive (damage)
A bridge can collapse when the amplitude of its vibration increases as a result of
resonance Tacoma Narrows Bridge at Puget Sound, Washington in 1940.
In an earthquake, buildings often vibrate in resonation
to seismic waves causing them to collapse.
1.2 ANALYSING REFLECTION OF WAVES
1. Reflection of a wave occurs when a wave strikes an obstacle
such as barrier, plane reflector, mirror and wall.
2. The reflection of waves obeys the law of reflection:
i. The angle of incidence, i is equal to the angle of reflection, r.
ii. The incident wave, the reflected wave and the normal all lie in the same plane.
Properties Of Water Waves After Reflection
Wavelength, Unchanged
Frequency, f Unchanged
Speed, v Unchanged
Velocity, v Changed
Direction of propagation of wave Changed according to the angle of incidence
3. Plane waves reflected by a concave barrier will converge to a focus.
4. Plane waves reflected by a convex barrier will diverge.
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1.2.1 Pattern of Reflected water waves
Reflection of Light Wave Reflection of sound waves
The angle of incidence, i is equal to the angle of reflection, r. 5
The Laws of Reflection is obeyed.
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1.2.2 Applications of Reflection of Waves in Daily Life
1. Safety: The rear view mirror and side mirror in a car. The mirrors reflect light waves from other
cars and objects into the driver’s eyes.
2. Defence: A periscope use in the submarine. The light waves from an object that is incident on a
plane mirror in the periscope are reflected twice before entering the eyes of the observer.
3. Telecommunications: Infrared waves from the remote control of electrical equipment are
reflected by objects in the surroundings and received by the television set or radio.
Working Principle of a Ripple Tank
1.3 ANALYSING REFRACTION OF WAVES
The refraction of waves occurs when there is a change of direction of the propagation of waves
travelling from a medium to another medium due to a change of speed.
Properties Of Refracted Deep Water to Shallow Water to
Water Waves Shallow Water Deep Water
Wavelength, Decreases Increases
Velocity, v Decreases Increases
Frequency, f Unchanged
v f f v constant v1 v2
1 2
Direction of propagation Bends towards Bends away from
of wave the normal the normal
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1.3.1 Refraction of Plane Water Waves
1. When the water wave travel from a deep area into shallow area, the direction of propagation of
the waves is refracted towards the normal.
2. The angle of incidence, i of the water is greater than the angle of refraction, r.
(a) (b)
Deep Shallow Deep Deep Shallow Deep
(c) Shallow Deep (d) Shallow Deep
Deep Deep
(e) (f)
Deep
Shallow Deep Deep Shallow Deep
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1.3.2 Refraction of Light Waves
Normal
1. When a ray propagates from one medium to an optically Air
Glass block
denser medium, the ray refracts towards the normal.
2. The speed of light decreases as it propagates in the glass
block (optically denser medium), causing it to alter the
direction of propagation.
1.3.3 Refraction of Sound Waves
1. On a hot day, the hot surface of the Earth causes the layer of air near the surface to be
warmer. This causes sound waves to be refracted away from the Earth.
2. On a cool night, the sound waves travel slower in the cooler layer of air near the surface of
the Earth than in the upper, warmer air. The waves are refracted towards the Earth.
3. Hence, sound can be heard over a longer distance on a cold night compared with a hot day.
4. A sound wave is refracted towards the normal when the wave passes from the air (less dense)
to the carbon dioxide (denser) in the balloon. The balloon acts as a convex lens that converge
the sound waves to the microphone.
5. If the balloon is filled with a less dense gas such as nitrogen or helium, the sound wave will be
refracted away from the normal when it passes from the air to the balloon. The balloon will act as
a concave lens in this case.
Temperature of Density of Gas Density of Medium
Air
Hot Cold Less Dense Denser Less Dense Denser
Speed of Sound Wave Faster Slower Faster Slower Slower Faster
Refraction of Sound Wave
Towards the normal Hot to Cold Less Dense to Denser Denser to Less Dense
Away from the normal Cold to Hot Denser to Less Dense Less Dense to Denser
Sound travels slower through denser gas because it particle’s mass is greater and inertia is greater.
Sound travels fastest through denser medium because the molecules are more tightly linked.
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1.4 ANALYSING DIFFRACTION OF WAVES
1. Diffraction of waves is a phenomenon in which waves spread out when they pass through a
gap or round a small obstacle.
2. The effect of diffraction is obvious (clearly seen) only if
i. The size of the aperture (gap) or obstacle is small enough.
ii. The wavelength is large enough (*the frequency is low).
Properties Of Water Waves After Diffracted
Wavelength, Unchanged
Frequency, f Unchanged
Speed, v Unchanged
The direction of propagation changed
the pattern of the waves changed
1.4.1 Diffraction of Water Waves
(b) Wider gap > λ
(a) Narrow gap ≤ λ (d) Wider obstacle > λ
(c) Narrow obstacle ≤ λ
When water waves travel through a small gap, its energy is dispersed through a
larger area. Hence, the diffracted waves will vibrate with smaller amplitude.
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1.4.2 Diffraction of light waves
1. Diffraction of light waves is barely noticeable because light has very short wavelength.
2. Light waves will be diffracted if:
(i) Light is propagated through a small slit or small pinhole (size is similar to
that of the light wavelength).
(ii) The light source is monochromatic light of one colour and therefore of
one wavelength only.
3. The wider middle bright fringe shows that the light waves diffracted after pass through a narrow
slit.
4. If the slit becomes wider, diffraction pattern becomes less distinct.
1.4.3 Diffraction of sound waves
1. A listener is able to hear the sound of the radio
although it is behind the wall (beyond his vision).
2. It is because the sound of the radio spreads around
the corner of the wall due to diffraction of sound.
Sound waves are more easily diffracted in comparison to light waves because the
wavelength of sound waves is much longer than the wavelength of light waves.
1.5 ANALYSING INTERFERENCE WAVE
1. Interference is the superposition of two waves from two coherent sources meet.
2. Two waves are in coherent if they are of the same frequency, amplitude and are in phase.
3. There are two types of interference:
i. Constructive interference Produce maximum resultant amplitude.
ii. Destructive interference Produce zero resultant amplitude.
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Mr Ng Han Guan Form 5 Chapter 1: Wave
Guru Cemerlang Physics MSAB
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1.5.1 Principle of Superposition
1. The principle of superposition states that when two waves overlap, the resultant displacement
is equal to the sum of the displacements of the individual wave.
2. Constructive interference occurs when the crests or troughs of both waves coincide to produce
a wave with maximum amplitude.
+= +=
Before superposition During superposition Before superposition During superposition
3. Destructive interference occurs when the crests of
one wave coincide with the trough of the other waves
to produce a wave with zero amplitude.
+=
Before superposition During superposition
1.5.2 Interference of Water Waves
1. Antinodal lines are lines joining antinodes, and
antinodes are points where constructive
interference occurs.
2. Nodal lines are lines joining nodes, and nodes are
points where destructive interference occurs.
3. Relationship between , a, x and D ax
D
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1.5.3 Interference of Light Waves
1. Same as water waves and sound waves also requires two coherent sources.
2. Two coherent light sources can produce with experiment, which is known as Young’s double-
slit experiment.
3. A ray of light passes through the single slit and reaches the double-slit will give rise to two
coherent light rays.
4. The superposition of these two rays produces constructive and destructive interference.
5. The formula, ax to determine wavelength of light waves. Where x is the distance between
D
two consecutive fringes (bright or dark). If the distance across 11 consecutive bright fringes is
measured that is, 10x.
L x = L / 10
11 consecutive bright fringes = L = 10 x
1.5.4 Interference of Sound Waves
1. Coherent sound waves interfere with each other to produce areas of louder sound
(constructive interference) and softer sound (destructive interference).
2. The formula, ax where x is the distance between two consecutive positions where a loud
D
sound or soft sound is heard.
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Mr Ng Han Guan Form 5 Chapter 1: Wave
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1.6 ANALYSING SOUND WAVES
1. Sound waves are longitudinal waves, which require a medium for its propagation.
2. Sound propagates in the form of compressions and rarefactions of air.
3. The wavelength of a sound wave is the distance
between two consecutive compressions or
rarefactions of air molecules.
4. Bell-jar experiment can shows that sound waves
cannot pass through vacuum.
5. Sound travels fastest through solid and slowest
through gas. This is because the molecules in a solid
are more tightly linked.
1.6.1 Properties of sound
1. The loudness of the sound is depends on the amplitude of the wave.
2. The pitch of the sound is depends on the frequency of the wave.
3. The quality of the sound is depends on the waveforms produced.
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1.6.2 Application of Sound Waves
1. Ultrasonic waves with frequencies above 20 kHz cannot be
heard by human ear.
2. Dolphins use ultrasound frequencies of about 150 kHz to
communicate with each other, to navigate and to find food.
3. An ultrasound beam is used in ultrasonic spectacles for blind people to know
that whether the object causing the echo is near or far away.
4. Echo is also used to detect flaws inside pieces of metal.
5. Doctors use ultrasound to obtain a
picture called a sonogram to see an
unborn baby. In order to see fine
details, the wavelength of the sound
waves must be short.
6. Sonar (Sound Navigation and Ranging) is used to determine the
depth of water and also used to detect underwater objects by
means of an echo.
7. The depth of sea water can be calculated using the
formula: t
d=vx 2
1.7 ANALYSING ELECTROMAGNETIC WAVES
The electric and magnetic field vibrate perpendicular to each other and to the direction of propagation.
1.7.1 Properties of electromagnetic waves
Transverse waves
Do not require a medium to propagate and can travel in a vacuum
The waves travel at the speed of light, c = f = 3 x 108 m s-1 through a vacuum
Undergo the same waves phenomenon : reflection, refraction, diffraction and interference
Have different frequencies and different wavelengths
Unaffected by external electric and magnetic fields
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1.7.2 Electromagnetic Spectrum
The range of frequencies and wavelengths over which electromagnetic waves are propagated.
Type of Source Application
electromagnetic wave
Electrical oscillating circuit Television transmission
Radio waves (SW, MW, LW, VHF, UHF) Telecommunications
= 10-1 ~ 105 m Communications in radio, airplanes and ships
- Mobile phone networks
Microwave Special electronic devices - Radar systems
= 10-3 ~ 10-1 m such as the klystron tube - Satellite transmissions
- Night vision
Infrared Hot bodies, the sun and - Thermal imaging and physiotherapy
= 10-6 ~ 10-3 m fires - Remote controls for TV
- Sight
Visible light The sun, hot objects, light - Photosynthesis in plants
= 10-7 m bulbs, fluorescent tubes - Photography
- Identification of counterfeit notes
Ultraviolet radiation Very hot objects, the sun, - Production of vitamin
= 10-9 ~ 10-7 m mercury vapour lamps - Sterilisation to destroy germs
- Radiotherapy
X-ray x-ray tubes - Detection of cracks in building structures
= 10-11 ~ 10-9 m - Can show the condition of a person’s bones
- Cancer treatment
Gamma rays Radioactive substances - Sterilisation of equipment
= 10-14 ~ 10-10 m - Pest control in agriculture
1.7.3 Effects of Electromagnetic Spectrum
1. Radio waves: harm body cells, prevalence of 5. Ultraviolet: damage to surface cells (including
migraine, headache disorders skin cancer) and blindness
2. Microwaves: internal heating of body tissue 6. X-rays: damage to cells
3. Infrared: skin burns 7. Gamma rays: cancer, mutation
4. Visible light: increased rates of premature skin
aging and skin cancer
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1.7.4 Wave in Telecommunication
1. Sound waves cannot travel far. So, a very efficient way to send a voice signal is by using the
carrier wave.
2. Modulation is the process where the sound signal is combined with the carrier wave.
3. The two most common types of modulation used in radio broadcasting are
i. Amplitude modulation (AM)
ii. Frequency modulation (FM)
1.7.5 FM and AM
1. FM waves have higher frequencies and more energy than AM waves.
2. FM waves penetrate the atmosphere instead of being reflected back to the Earth.
3. FM waves do not travel as far as AM waves.
4. FM waves are usually received clearly and produce a better sound quality than AM waves.
5. Wideband FM receivers are inherently less sensitive to noise.
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Mr Ng Han Guan Form 5 Chapter 2: Electricity Date:
Guru Cemerlang Physics MSAB
CHAPTER 2: ELECTRICITY
2.1 CHARGES AND ELECTRIC CURRENT
2.1.1 Van de Graaff Generator
1. Van de Graaff generator can accumulate very high charges on its dome.
2. Van de Graaff generator in action:
3. When the accumulated charges on the dome flow to
the ground, there is a momentary flow of current.
4. They are two types of charges:
Positive charge Negative charge
5. The lines and patterns represent the electric field. An electric field is a regional space where
any particles experience electric forces.
6. Like charges repel. Unlike charges attract.
7. The flow of electrical charges produces electric current.
2.1.2 Electric Current
1. Electric current can be defined as the rate of electric charge flow (flow of electrons).
2. Electric current = rate of electric charge flow
Quantity of charge flow , Q Unit : - Q is coulomb (C)
Time taken, t - A is ampere (A)
- t is second (s)
I Q Q It
t 1 C = 1 A s 1 A = 1 C s -1
3. If one coulomb of charge flows past in one second, then the current is one ampere
4. 15 amperes means in each second, 15 coulomb of charge through a cross section of a
conductor.
5. In a metal wire, the charges carried are electrons.
6. Each electron carries a charge of 1.6 x 10-19 C.
7. 1 C of charge is 6.25 x 1018 electrons.
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2.1.3 Electric Field
1. An electric field is a region in which an electric charge experiences a force.
2. An electric field can be represented by a number of lines indicate both the magnitude and
direction of the field
3. The principles involved in drawing electric field lines are :
(i) electric field lines always extend from a positively-charged object to a negatively-charged
object to infinity, or from infinity to a negatively-charged object,
(ii) electric field lines never cross each other,
(iii) electric field lines are closer in a stronger electric field.
EFFECT OF AN ELECTRIC FIELD ON A CANDLE FLAME
Observation: Explanation:
The candle flame splits into two portions in The heat of the flame ionizes the air molecules
opposite direction. The portion that is
attracted to the negative plate is very much to become positive and negative charges.
larger than the portion of the flame that is The positive charges are attracted to the
attracted to the positive plate.
negative plate while the negative charges are
attracted to the positive plate.
The flame is dispersed in two opposite
directions but more to the negative plate.
The positive charges are heavier than the
negative charges. This causes the uneven
dispersion of the flame.
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2.2 THE RELATIONSHIP BETWEEN ELECTRIC CURRENT AND POTENTIAL DIFFERENCE
2.2.1 Ideas of Potential Difference
Similarly
1. The charges then transport the energy to the bulb.
2. The energy is higher at the beginning, and then it becomes weaker as it gets closer to the
battery.
3. This is similar to the men in the picture.
4. They are full of energy at the beginning to climb the mountain but lose their energy after the
climb.
5. Then, they return to eat and drink to regain their energy.
6. The charges with less energy return to the battery to
collect more energy.
7. Electric potential at A is greater than the electric potential
at B.
8. Electric current flows from B to A, passing the bulb in the
circuit and lights up the bulb.
9. This is due to the electric potential difference between
the two terminals.
10. As the charges flow from A to B, work is done when electrical energy is transformed to light and
heat energy.
11. The potential difference, V (voltage) between two points in a circuit is defined as the amount
of work done, when one coulomb of charge passes from one point to the other point in an
electric field.
Potential difference,V Work done, W W , SI unit : Volt (V)
Quantity of change, Q Q
12. Potential difference can be measured by a voltmeter.
13. To measure the p.d. across the conductor such as the resistor, the voltmeter must be connected
in parallel to it, as shown in the diagram.
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Cells
2.2.2 Device and symbol
Ammeter A
Voltmeter V Switch
Constantan wire //
Connecting wire eureka wire
Bulb
Resistance
Rheostat
2.2.3 Measuring Current and Potential Difference/Voltage
Measurement of electricity Measurement of potential difference/voltage
(a) Electrical circuit (a) Electrical circuit
(b) Circuit diagram (b) Circuit diagram
2.2.4 Ohm’s Law
The current that passes through an ohmic conductor is directly proportional to the potential
difference applied across it, if the temperature and other physical conditions are constant.
V I V constant = R
I
*An ohmic conductor is a conductor that
obeys Ohm’s Law.
*A non-ohmic conductor is a conductor that does not obeys Ohm’s Law.
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1. The constant is known as resistance, R of the conductor.
2. The resistance, R is a term that describes the opposition experienced by the electrons as they flow
in a conductor.
3. It is also defined as the ratio between the potential difference and the current, I. That is
V V=IR
R= I
4. The unit of resistance is volt per ampere (V A-1) or SI unit:
ohm, 1 = 1 V A-1
2.2.5 Factors Affecting Resistance
1. The factors affecting the resistance of a conductor:
(i) the length of the conductor directly proportional
(ii) the cross-sectional area of the conductor inversely proportional
(iii)type of material of the conductor eureka > constantan > copper
(iv)the temperature of the conductor increases gradually
R 1 & Rl
A
l R l
2. Combining both equation, we obtain R A
A
3. is a property of the material of the conductor called as resistivity. The unit for is m.
Factors Diagram Hypothesis Graph
Length of the The longer the conductor, the
conductor, l higher its resistance.
The cross- The bigger the cross-sectional
sectional area of area, the lower the its resistance
the conductor, A
The type of the Different conductors with the same
material of the physical conditions have different
conductor resistance
The temperature The higher temperature of
of the conductor conductor, the higher the
resistance
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2.2.6 Superconductors
1. The electrical resistivity (resistance) of a metallic conductor decreases gradually as the
temperature is lowered.
2. However, in ordinary conductors such as copper and silver, this decrease is limited by impurities
and other defects. Even near absolute zero, a real sample of copper shows some resistance.
3. Despite these imperfections, in a superconductor the resistance drops abruptly to zero when the
material is cooled below its critical temperature, TC.
4. Superconductivity is an electrical resistance of exactly zero which occurs in certain materials
below a certain critical temperature, TC.
5. An electric current flowing in a loop of superconducting wire can persist indefinitely with no power
source.
6. It was discovered by Heike Kamerlingh Onnes in 1911 when he cooled mercury to below 4.2 K.
(a) Normal conductor (b) Superconductor
2.2.6.1 Applications of Superconductors
1. Cable or wires made of superconductors will increase the efficiency of electrical power
transmission as the loss of energy in the form of heat is greatly reduced.
2. Electrical energy can be stored in superconducting coils for future use and there will be no
energy loss in superconducting electrical power lines.
3. Superconductors can make electric cars more feasible and computer much faster.
4. Another important and useful application is superconducting magnets which would make things
like magnetic levitation (MAGLEV) trains and medical imaging (MRI) scanner more economical.
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2.3 SERIES AND PARALLEL CIRCUITS
PARALLEL CIRCUIT
SERIES CIRCUIT
I is constant. I = I2 + I3
V = V1 + V2 + V3 V = V1 = V2 = V3
IR = IR1 + IR2 + IR3 I = V/R
IR = I(R1 + R2 + R3)
R = R1 + R2 + R3 I = I1 + I2 + I3
V/R = V/R1 + V/R2 + V/R3
2.3.1 Identify Series Circuit or Parallel Circuit V(1/R) = V(1/R1 + 1/R2 + 1/R3)
1/R = 1/R1 + 1/R2 + 1/R3
Series Parallel A, B - Series Q, S - parallel
C and (A, B) - parallel P and (Q, S) - Series
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2.3.2 Effective resistance, R
R = 20 + 10 + 5 = 35
1/R = ½ + 1/5 + 1/10 = 4/5
Effective R = 1.25
1/R = 1/8 + 1/8 = 2/8 = 1/4 1/R = 1/(8 + 8) + 1/8 + 1/(4 + 4) = 5/16
R=4 Effective R = 3.2
Effective R = 20 + 10 + 4 = 34
1/R = 1/5 + 1/(5 + 5) = 3/10 1/R = 1/10 + 1/20 = 3/20
R = 3.33 Effective R = 20/3 + 8 = 14.67
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2.4.1 Electromotive force
1. The free electrons in a wire AB are moving around
and will not flow unless they are forced to do so.
2. A battery or generator connected to the wire AB can
provide a force which will cause the electrons to flow.
3. This is called electromotive force. The electromotive
force creates an electrical “pressure” difference
across AB.
4. An electric current will then flow from the positive
terminal through AB, back to the negative terminal
and repeat the cycle as shown in Diagram A.
5. Note that the free electrons flow in the opposite
direction to the conventional current as shown in
Diagram B.
6. When the circuit is completed, chemical changes take place in the battery and they produce
the energy required to push an electric charge (electrons) „round‟ the circuit.
7. We can define electromotive force (e.m.f.) of a battery
as equal to the electrical energy provided by the
battery for every coulomb of charge which flows
‘around’ the circuit.
e.m.f., E = Energy provided, W/Charge, Q
E = W/Q, SI unit: Volt, V (J C-1)
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2.4.2 Relationship between Electromotive Force and Potential Difference
Figure (a) Figure (b)
Electromotive force, e.m.f., E
= VR + Vr where VR = IR and Vr = Ir
E = IR + Ir or V = E - Ir
E = I (R + r) r = internal resistance
1. If an ideal e.m.f. source is connected to a circuit of total load
resistance R as shown, the total electric power will be
available on the load. Thus, from the definitions, we can define
that the external potential difference generated will be
equal to the e.m.f. of the source.
2. But for a practical source of e.m.f., not all the total
electrical power generated is usefully available to the
external load of resistance R.
3. Part of the total electrical power is spent to overcome the
inherent internal resistance r of the source. In this case,
we will find that the potential difference across the load R
is less than the e.m.f. value of the source.
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2.5 ELECTRICAL ENERGY AND POWER
2.5.1 Electrical Energy
1. Electrical energy is defined as the ability of the electric current to do work. It is a form of
energy produce by the flow of electrons.
2. Electrical energy supplied from an electric source will be transformed to other type of energy
when current flows through a closed circuit.
3. Potential difference, V across two points is the energy, E dissipated or transferred by a
coulomb of charge, Q that moves across the two points.
E = VQ Q = It
E = VIt SI unit: joule, J
2.5.2 Electrical Power
Power is defined as the rate of energy transforms from one type to another.
P = VI SI unit: watt, W (1 W = 1 J s-1)
Electrical Energy, E Electrical Power, P
From the definition of potential difference, V Power is the rate of transfer of electrical energy,
SI unit : Joule (J) SI unit : Watt (W) // Joule per second (J s-1)
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2.5.3 Power Rating and Energy Consumption of Various Electrical Appliances
1. The amount of electrical energy consumed in a given period of time can be calculated by
Energy consumed = Power rating x Time
E = Pt where: energy, E is in Joules
power, P is in watts
time, t is in seconds
2. The unit of measurement used for electrical energy consumption is the kilowatt-hour, kWh.
1 kWh = 1000 J s-1 x 3600 s
= 3.6 x 106 J
= 1 unit
3. One kilowatt-hour is the electrical energy dissipated or transferred by a 1 kW device in one
hour.
4. Household electrical appliances that work on the heating effect of current are usually marked
with voltage, V and power rating, P.
5. The energy consumption of an electrical appliance depends on the power rating and the
usage time, E = Pt
2.5.4 Cost of energy Power / kW Time Energy Consumed
Appliance Quantity Power / W 0.06 8 hours (kWh)
0.4
Bulb 5 60 1.5 0.48
Refrigerator 1 400 1.0
1 1500 24 hours 9.6
Kettle 1 1000
Iron 3 hours 4.5
2 hours 2
Total energy consumed, E = (0.48 + 9.6 + 4.5 + 2.0)
= 16.58 kWh
Cost = 16.58 kWh x RM 0.28
= RM 4.64
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2.5.5 Energy Efficiency
1. Efficiency is defined in percentage as the ratio of useful power output to power input, that
is
2. A tungsten filament lamp changes electrical energy to
useful light energy and unwanted heat energy
Efficiency of a filament lamp:
= (3/60) x 100 %
= 5%
3. A fluorescent lamp or an „energy saving lamp‟ produces
less heat than a filament lamp for the same amount of
light produced.
Efficiency of a fluorescent lamp and an „energy saving
lamp‟
= (3/12) x 100 %
= 25 %
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CHAPTER 3: ELECTROMAGNETISM
3.1 MAGNETIC EFFECT OF A CURRENT-CARRYING CONDUCTOR
3.1.1 Electromagnets
1. Electric and magnetic fields occur naturally wherever there is electricity.
2. Electric fields are produced by electrically charged objects.
3. A bar magnet produces the magnetic fields around it. The magnetic fields of a magnet cannot
be “switched off”.
4. Magnetic fields also can be produce by an electric current in a wire
5. The experiment above shows that a magnetic field is produced when current flows through a
wire.
6. When the direction of the current is reversed, the compass needle deflects in the opposite
direction.
7. This is called electromagnet. Electromagnet is a temporary magnet.
3.1.2 The Magnetic Field Pattern of a Current-carrying Straight Wire
1. When the switch is on, the resulting magnetic field lines are series concentric circles around
the wire.
2. The Right-hand Grip rule can be used to determine the direction of the magnetic field.
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3.1.3 Right-hand Grip Rule for Current-carrying a Straight Wire
1. Right-hand Grip Rule states that the thumb of the right hand points to the direction of current
flow and the other four curled fingers will curl the same way as the direction of the magnetic
field.
2. As the direction of the current is reversed, the direction of the magnetic field will also be
reversed.
Magnetic field patterns from the top views
Means that a wire carrying current
into the plane of paper.
Means that a wire carrying current
out of the plane of paper.
3. The strength of the magnetic field represented by field lines that show the shape of the field.
4. Magnetic field lines which are close together represent a strong field.
5. The strength of the magnetic field is greater when it is closer to the wire.
6. The strength of the magnetic field also depends on the magnitude of the current flowing through
the wire.
7. The larger the magnitude of the current, the greater the strength of the magnetic field.
*Maxwell’s Screw Rule also can use to determine the direction of the magnetic field around a wire.
3.1.4 Right-hand Grip Rule for Current-carrying in a Coil
1. The magnetic field is stronger at the centre of the coil.
2. This means that more magnetic field lines per unit area lie
on the inside region of the coil.
3. Note that the field lines at the centre are straight and
perpendicular to the plane of the coil.
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4. The strength of the magnetic field can increase by increasing the current.
5. We can also increase the number of turns of the flat coil.
3.1.5 Right-hand Grip Rule for Current-carrying in a Solenoid
1. We can use a small compass to find the direction of the magnetic field.
2. The magnetic field of a solenoid has the same shape as the magnetic field around a bar magnet.
3. Hence, the solenoid can be said to have
poles.
4. If the current is flowing in a clockwise
direction, it shows the end of the coil is the
South Pole.
5. If the current is flowing in an anticlockwise
direction, it shows the end of the coil is the
North Pole.
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6. The strength of the magnetic field can be increased by:
a. Increasing the current,
b. Increasing the number of turns per unit length of the solenoid,
c. Placing an iron core within the solenoid.
7. However, the strength of the magnetic field decreases with distance from a current-carrying
source.
3.1.6 Applications of Electromagnet
1. Electromagnet is a temporary magnet; it can be switch “on” and “off”. This makes them very
useful.
2. Electromagnets are used to make electric bells,
electromagnetic relays and many others.
3. Iron is used to make electromagnets because
unlike steel, it can be easily magnetised and
demagnetised.
3.1.6.1 Electric Bell 33
1. When the button is depressed, current flows through the coil.
2. The electromagnet (soft iron and coil of wire) attracts the soft iron armature.
3. The hammer hits the gong.
4. When the hammer moves towards
the gong, the contact opens.
5. The circuit is broken at S and the
current stops flowing.
6. The iron core in the electromagnet
loses its magnetism and it no
longer attracts the armature.
7. The metal strip (spring) returns to its original position, completing the circuit again.
8. Current flows in the circuit and the process is then repeated.
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3.1.6.2 Electromagnetic Relay
1. A relay is a switch that is operated by an electromagnet.
2. There are two separate circuits.
3. The first circuit is for the electromagnet and the second circuit is for the electric motor.
4. A small current in the electromagnet circuit is used to
switch on a large amount of current in the motor circuit.
5. When S is switched ON, the current flows in the coil and
the coil becomes magnetised, attracting the soft iron
armature.
6. The movement of the iron armature closes the contacts
and the electric motor is switched on.
7. A relay is used to switch on a large amount of current
through the use of a smaller current. This is useful for two reasons:
a. First circuit may contain a component such as a light detecting resistor (LDR), which only
uses small currents,
b. Only the circuit with a large current need to be connected with thick wire.
8. Examples of these are start the car engine, automatic doors and computer.
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3.1.6.3 Telephone Earpiece
1. A varying current received from the caller in
3.1.6.4 Circuit Breaker telephone line.
2. The varying current passes through solenoid
and magnetized the soft-iron core.
3. The electromagnet varies in magnetic strength
according to the verifying current.
4. The alloy diaphragm will attract to
electromagnet by varying force.
5. Sound produced as compression and
rarefaction of air particles.
1. It operates as automatic switch to breaks circuit
to open when current becomes too large.
2. When the current becomes high (eg: short circuit)
the electromagnet strength increase suddenly.
3. The iron catch is pulled toward electromagnet.
4. The spring pulling apart the contacts.
5. The circuit will break and the current flows stop
immediately.
6. The system can be reset when the reset button is
pressed. Spring pulls the soft iron armature back
to its original position and the contacts close again.
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3.2 THE FORCE ON A CURRENT-CARRYING CONDUCTOR IN A MAGNETIC FIELD
We have seen that an electric current produces a magnetic field around it. So it is not surprising to find
that when a wire carries an electric current through another magnetic field, the two magnetic fields
interact and produce a force on the wire.
1. The figure shows a copper rod, which is placed on a pair of copper rails between the poles of the
two magnets.
2. When the switch is on, we can observe that the copper rod moves to the right.
3. We can deduce that the current-carrying conductor experiences a force when placed in
magnetic field.
4. There is an interaction between the magnetic field of the current-carrying copper rod and the
magnetic field of the permanent magnet.
5. This will lead to a force being experienced by the conductor.
6. When the direction of the current is reversed, the direction of the force exerted on the copper
rod is also reversed.
7. The force is at right angles to the other two directions:
a. Direction of the current.
b. Direction of the magnetic field.
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3.2.1 Fleming’s Left-hand Rule
1. We can deduce the direction of the force on the current-carrying wire by means of Fleming’s
Left-hand Rule.
2. The forefinger represents the direction of the
magnetic field (N to S pole).
3. The second finger represents the direction of the
current (+ve to –ve).
4. The thumb represents the direction of the motion of
the wire (force).
5. If the forefinger points in the direction of the
magnetic field and the second finger the
direction of the current in the wire, then the
thumb will point in the direction of the force
on the conductor.
6. To obtain a maximum motion (maximum
force) the direction of the current must
be perpendicular to the direction of the
magnetic field.
7. If the direction of the current and direction of
the magnetic field are parallel, there will be no
force exerted on the wire.
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3.2.2 Catapult Field
1. Fleming’s Left-hand Rule only helps us predict the direction of force exerted on the wire.
2. We can explain the origin of the force by examining the combined magnetic field of the wire
and the magnet.
3. Figure A shows the magnetic field of the
magnet and the magnetic field of the current-
carrying wire separately.
4. Figure B shows the combined magnetic field
when the wire is placed between the poles of
the magnet.
5. When the two fields are combined, a complex
field pattern is produced.
6. If free to move, it will be catapulted from the stronger field towards the weaker field or a
neutral point.
7. We can see that there is a stronger field on one side of the wire at A.
8. At B, the magnetic field is weaker.
9. A force will then act on the wire in the direction as shown in Figure B.
10. This type of unbalance magnetic field is called a catapult field.
11. When the direction of current is
reversed, the direction of the force is
also reversed.
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3.2.2.1 Forces between Two Parallel Current-Carrying Wires
1. If currents pass along two parallel wires, each wire will set up a magnetic field and the fields will
interact with each other.
2. If the two parallel wires have current flowing in the same direction, they will attract each other.
3. On the other hand, if they have current flowing in opposite directions, they will repel each other.
3.2.2.2 Forces on a Current-Carrying Rectangular Coil in a Magnetic Field
1. When a current passes through the loop, we will find that there is a turning force on the wire loop.
2. The loop will turn about the axis PQ.
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3. The wire AB will have force acting on one side while the
force on wire CD is acting on the other side.
4. These two forces produce a turning effect, which turns
the loop clockwise.
5. If the magnet or the battery is reversed, the directions of
the forces are also reversed.
6. This turning effect on a loop of current-carrying wire
has a very important application the motors.
3.2.2.3 The Direct Current Motor (D. C. Motor)
1. The ends of the wire are connected to split rings X
and Y, the commutator.
2. The commutator rotates with the loop.
3. Two carbon brushes are made to press lightly against the commutator.
4. The rectangular loop ABCD of wire is mounted on an axle that will allow it to
rotate about the axis PQ.
5. When the current flows through the loop ABCD, a downward force would
act on the left-hand side AB, and an upward force on the right-hand side CD.
6. The loop would then rotate about axis PQ until it reaches the vertical position.
7. The current is now cut off but the momentum and inertia of the loop carries it past the vertical
position.This reverses the current in the wire arm CD and now a downward force acts on it.
8. An upward force now acts on the other wire arm AB.
9. Hence, the loop continues to rotate in the same direction.
10. The commutator is there to reverse the direction of the current in
the loop whenever the commutator changes contact from one
carbon brush to the other.
11. This ensures that the loop will always be turning in one direction.
12. When the terminal of the battery is reversed the direction of the rotation of the loop will be
reversed.
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3.2.2.5 Factors that affect the speed of rotation of an electric motor
To increase the turning effect or rotation speed of the wire loop, we can
a. Increase the number of turns of the wire in the rotating coil,
b. Increase the current,
c. Use a stronger magnet to strengthen the magnetic field,
d. Place a soft-iron core within the magnetic field lines to strengthen the magnetic
field.
3.2.2.6 Moving Coil Ammeter
The angle of deflection The hair spring
is directly proportional will restore the
to the current flows in pointer back to
the coil its original
position.
The force acting causes
the coil to rotate and
lead the pointer to the
deflection
When current flows in
moving coil, magnetic
field of radial magnet
will interacts with
magnetic field produce
by the coil
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3.3 ELECTROMAGNETIC INDUCTION
1. When the metal rod move upwards through the strong magnetic field, we can see there is
deflection of the needle of galvanometer.
2. The deflection of the needle shows the direction of
the current flows in the wire.
3. That current calls Induced Current.
4. Induced Electromotive Forces (Induced e.m.f.)
are induced on a coil whenever the magnetic flux
through the coil changes.
5. Induced current can be produced in a wire simply by
moving a magnet in or out of the coil.
6. No battery or other voltage source is needed.
7. This relative movement between the conductor and the magnetic field changes the magnetic flux
and induces a current and a voltage on the conductor. This phenomenon is called
electromagnetic induction.
8. The magnitude of the induced e.m.f. and direction of the induced current can be determined by
application of the laws of electromagnetic induction:
a. Faraday’s Law
- To determine the magnitude of the induced e.m.f.
b. Lenz’s Law
- To determine the direction of the induced current.
3.3.1 Faraday’s Law of Electromagnetic Induction
1. The magnitude of the induced electromotive force (e.m.f.) is directly proportional to the rate of
change of magnetic flux (which the conductor cuts the magnetic fields lines).
2. Hence, the magnitude of the current increases with:
a. The speed of motion.
b. The number of turns on the coil.
c. The strength of the magnet.
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3.3.2 Lenz’s Law
1. The direction of the induced e.m.f. (electromotive force) is such that its magnetic effect always
opposes the change which produces it.
2. The direction of the induced current opposes the change that produces it.
3. The strength of the magnetic field at the solenoid increases as the magnet moves towards it,
and it is seen that the flowing current makes end A the North Pole.
4. If the magnet moves away from the solenoid, current will flow in the opposite direction and end A
now becomes the South Pole. It opposes the motion of the magnet.
5. The direction of induced current can be determined using Fleming’s Right-hand Rule (Dynamo
Rule).
3.3.3 Applications of Electromagnetic Induction
1. A generator is essentially the opposite of a motor which
converts mechanical energy into electrical energy.
2. A simple generator consists of a rectangular coil
rotating in a stationary magnetic field.
3. The generator produces electrical energy in the loop
when it is rotated in the magnetic field.
4. As the speed of rotation of the coil increases, the
induced voltage also increases.
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3.3.3.1 Direct Current Generator (D.C. Generator)
1. At a vertical position, the coil moves in parallel with the
magnetic field.
2. When there is no conductor cutting the magnetic lines of
force, the induced current is zero.
3. When the coil rotates from a vertical to a horizontal
position (90o), the current induced in the coil
increases from zero to maximum.
4. The direction of the current induced can be
determined by Fleming’s Right-hand Rule.
5. When the coil rotates to a vertical position again
(180o), the current induced will decreases from
maximum to zero.
6. At a horizontal position (270o), the current
induced in the coil will flow in the reverse
direction.
7. The position of the commutator changes, therefore the current flowing in the external circuit is
always in the same direction.
8. The magnitude of the induced e.m.f. depends on the position of the rotating coil.
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3.3.3.2 Alternating Current Generator (A.C. Generator)
1. An alternating current (a.c.) generator can be
modified from a d.c. generator by replacing the
commutator with two copper slip-rings.
2. The magnetic flux through the coil changes when
the coil rotates and electromotive force (e.m.f.) is
induced on the coil.
3. As the loop rotates, there is a change in the number of magnetic lines of force it encloses.
4. The number varies from a maximum to a minimum and back to a maximum again, depending on
the position of the loop.
5. If we double the number of turns on
the coil without changing the
frequency of rotation of the coil, the
output voltage V waveforms will be as
shown in the diagram.
6. If we double the frequency of rotation of the
coil without changing the number of turns
on the coil, the maximum output voltage
will also double as shown in the diagram.
7. The induced e.m.f. of an a.c. generator can
also be increases by:
a. Using stronger magnetic fields
b. Winding the coil on a soft-iron core to concentrate the magnetic lines of force through the
coil. 45
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Alternating Current
Direct Current
1. An alternating current (a.c.) is an electrical 1. Direct current (d.c.) is the continuous flow of
current. electric current through a circuit from the
higher potential to the lower potential.
2. The magnitude and direction of the alternating
current varies cyclically. 2. In a direct current circuit, electric charges
always flow in the same direction.
3. Our houses are normally supplied with
alternating current by an a.c. generator. 3. Direct current (d.c.) is the type of electricity
stored in batteries or solar electric
4. The alternating current reverses direction very devices.
rapidly, for example, at 50 times a second
(50Hz) for our household electrical supply. 4. D.C. is commonly found in many low-
voltage electrical appliances, especially for
5. The usual waveform of an a.c. power circuit is a those powered by batteries.
sine wave.
3.4 TRANSFORMER
A step-up A step-down
transformer in a transformer near
a housing estate
power station
1. A transformer usually consists of a soft-iron 4. The flux linkage of the secondary coil is
core which is wound with two separate coils of constantly changing.
insulated wire. 5. So, an alternating voltage is induced across it.
2. One coil is called the primary coil and the 6. For a step-up transformer, the number of
other is the secondary coil. turns on the primary coil is less than that on
3. An alternating current that flows in the primary the secondary coil.
coil produces an alternating magnetic field in 7. For a step-down transformer, the number of
the soft-iron core. turns on the primary coil is more than that on
the secondary coil.
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In the case of an ideal transformer where no energy is loss:
3.4.1 Ways to Reduce Power Loss in Transformers
Practically, the efficiency of a transformer can never be 100%. This is due to the power lost during
transmission of a.c. supply from the primary circuit to the secondary circuit.
Causes of Power loss Way to Increases efficiency of a Transformer
The heating effect of the current in the Use thicker copper wires which have lower
copper wires of the coils. [Power loss = I2 R] resistance.
Eddy currents* induced in the iron-core will Use a core made of thin sheets which are
move in circles and heat up the core. laminated and insulated.
The loss of energy in the process of changing Use a soft-iron core so that it can be
the magnitude and direction of magnetic field magnetised and demagnetised easily.
in the core.
Flux leakage because the magnetic field lines Wind the insulated coils one on top of the
produced by the primary coil are not other.
completely linked to the secondary coil. The soft-iron core must always form a closed
loop of iron.
*Eddy currents, which are loop currents, flow radically and will dampen the flow of current. 47
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3.5 GENERATION AND TRANSMISSION OF ELECTRICITY
3.5.1 National Grid Network
1. National Grid Network is a network of underground cables or pylons which connect all the power
stations and substations for the whole country.
2. This network starts at electrical power plant like Chenderoh Lake Power Station which is
hydroelectric power station, and end at our houses.
3. Electrical energy is transmitted from the power station to the consumer using long transmission
cables. This will bring to power loss as heat energy.
4. The power loss can reduce by:
i. Reducing the resistance of the cables
ii. Reducing the current
iii. Increasing the voltage in the cable.
5. Power loss can be calculate as follow:
Pheat I 2R I = current flows in the cable
R = resistance of the cable
Renewable energy
1. Energy plays a very important role in economic development but the reserves of fossil fuels such
as oil and gas are very limited.
2. Hence, there is modern trend of the nations that is to harness the renewable energy.
3. Renewable energy sources are continually replenished naturally means they are sustainable.
4. The example of renewable energy:
Hydroelectric Solar Biomass Wind
Wave Tidal Geothermal
1. The example of non-renewable energy: Fossil fuel such as oil, gas and coal.
2. The benefits of using the renewable energy to our nation:
a. Avoid depletion of fossil fuels c. Avoid harming flora and fauna
b. Cleaner sources for little pollution d. Avoid the disruption of ecological balance
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3rd edition © 2011 | chp 3 | Maktab Sultan Abu Bakar | Sekolah Kluster Kecemerlangan
Mr Ng Han Guan Form 5 Chapter 4: Electronics Date:
Guru Cemerlang Physics MSAB
CHAPTER 4: ELECTRONICS
4.1 CATHODE RAY OSCILLOSCOPE (C.R.O)
4.1.1 Thermionic Emission
1. Diode is an apparatus consists of a glass bulb that contains two
metal electrodes (anode and cathode) in a vacuum.
2. The cathode is a filament which can be heated.
3. An ammeter and a battery are connected across the diode as
shown in the diagram. When switch is on, current does not flow
through the ammeter.
4. A 9 V battery connect across the cathode filament so that it is
heated. Current flow through the ammeter when the cathode is
hot.
5. This process is called thermionic emission.
6. Thermionic emission is the emission of electrons from the
surface of a heated metal.
7. The current that passes through the tungsten filament heats it up.
8. The heat gives off enough kinetic energy to the electrons in the tungsten to escape from its
surface.
9. The emitted electrons are accelerated to the anode by the potential difference between the anode
and cathode.
10. The electron beam that speeds in the vacuum tube is called the cathode ray as it is produced
from the cathode.
11. Factors that influence the rate of thermionic emission
Factor Effects on thermionic emission process
Cathode voltage The rate of thermionic emission increases with an increased
cathode voltage due to a larger current and heat produced.
Cathode surface area The rate of thermionic emission increases with increased
cathode surface area.
Potential difference between The velocity of electrons increases with increased potential
anode and cathode difference between the anode and cathode.
3rd edition © 2011 | chp 4 | Maktab Sultan Abu Bakar | Sekolah Kluster Kecemerlangan 49
Mr Ng Han Guan Form 5 Chapter 4: Electronics
Guru Cemerlang Physics MSAB
Date:
4.1.2 Properties of Cathode Ray
1. Cathode Ray Tube is the glass bulb has a cathode with an anode close to it.
2. The anode has a hole in it so that when it is positive and attracts electrons, some electrons will
pass through the hole. This arrangement is called an electron gun.
3. The stream of electrons leaving the cathode and shooting across the vacuum are called cathode
rays.
4. When an electron beam passes between the two plates, the electrons are deflected towards the
positive plate. This is because those electrons are attracted by the positive charges on the
positive plate and are repelled by the negative charges on the negative plate.
5. The electron beam is also deflected by the magnetic field. This deflection can be determined by
using Fleming’s left-hand rule.
4.1.3 Change of Electron Energy in Cathode Ray
1. The potential difference between the anode and the cathode
gives potential energy to the electrons.
Electron potential energy = eV
|| e = 1.6 x 10-19 C || V = potential difference ||
2. The potential energy of the electron is converted into kinetic energy when it accelerates.
Kinetic energy = ½ mv2
|| m = electron mass = 9.1 x 10-31 kg || v = electron velocity ||
3. By the principle of conservation of energy,
Kinetic energy gained = potential energy lost
½ mv2 = eV electron velocity, v =
E.g.: In a vacuum tube, a cathode ray is produced and accelerated through a potential difference of
2.5kV.
Calculate…
(a) The initial electric potential energy of the cathode ray.
(b) The maximum velocity of the electron.
-19 -31
[e = 1.6 x 10 C; m= 9 x 10 kg]
Solution:
(a) Electric potential energy eV 1.6 10-19 2.5 103 4 1016J
(b) 1 mv2 eV 4 1016 v2 4 1014 2 v 8.89 1016 2.98 107m s-1
2 9 1031
3rd edition © 2011 | chp 4 | Maktab Sultan Abu Bakar | Sekolah Kluster Kecemerlangan 50