PHYSICS IGCSE REVISION GUIDE FOR CANDIDATES MRSM AG 2020

Program Stream AG #1 Physics IGCSE 2020

The refractive index (n)of an object determines how the light bends or changes
speed when it enters the object.

The refractive index (n)of an object can be found using the equations :

n = or n =

Remember the speed of light in medium 1 is generally 3 x 108 m/s .

Example 2

 Find the refractive index of
substance B.

Please note that the angle of refraction is
90° - 60° = 30°

n = sin i/sin r
n = sin 50/sin 30
n= 1.53

 What is the speed of light in substance B? Substance A is air.
n=

1.53 = 3 x 108/x
x = 3 x 108/1.53
x = 196078431 m/s

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Program Stream AG #1 Physics IGCSE 2020

Total Internal Reflection

i <cr  Explain the diagram using
the terms critical angle and
total internal reflection.

i = cr When i <cr the light refracts
through the medium.

i > cr When i =cr the light refracts at
an angle of 90°

When i >cr total internal
reflection takes place

Describe the application of total internal reflection in fibre optics.

Fibre optic cable uses the idea of total internal
reflection. Light is pass with the angle of
incidence that is greater than the critical
angle.

In communications this cable can pass
messages from one place to another in form
of light rays.

In the medical field the cable is used as an endoscope to help see the digestive tracks
during surgical operations.

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Example 3 Program Stream AG #1 Physics IGCSE 2020

answer
answer

Lenses

F is called the focal point. f is the focal length.

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Program Stream AG #1 Physics IGCSE 2020

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Program Stream AG #1 Physics IGCSE 2020

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Program Stream AG #1 Physics IGCSE 2020

Dispersion

When white light is passed
through a triangular prism it
breaks into its seven colours.
R(red)-least bent. Lowest
frequency-Highest λ
O (orange)
Y(yellow)
G(green)
B(blue)
I(indigo)
V(violet) most bent. Highest
frequency- Lowest λ

Electromagnetic spectrum

All electromagnetic radiation travel at
3 x 108m/s. They can travel through a
vacuum.

Notice that Gamma rays are the most
energetic and have the highest
frequency and lowest wavelength.

Radio waves are the least energetic
and have the lowest frequency and
highest wavelength.

Gate X Usually Lets In Most Radiation
You need to be able to:

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Program Stream AG #1 Physics IGCSE 2020

•Describe the role of electromagnetic waves in:
– radio and television communications (radio
waves)
– satellite television and telephones
(microwaves)
– electrical appliances, remote controllers for
televisions and intruder alarms (infrared)
– medicine and security (X-rays)

• Demonstrate an awareness of safety issues regarding the use of microwaves and X-rays

Monochromatic refers to light of a single frequency and colour.

Sound

Sound is produced by a vibrating source. Eg. A
vibrating violin string.

Describe how longitudinal sound
waves are produced.

The vibrating speaker causes
the air molecules to vibrate.
The low pressure regions
where the air molecules are
far apart are called
rarefactions. The high
pressure regions where the
air molecules are close are
called compressions

State the approximate range of audible frequencies- We can hear sound from the
frequency of 20Hz to 20kHz. We cannot hear any sound above 20kHz( ultra sound)

Show an understanding that a medium is needed to transmit sound waves
Sound cannot travel in a vacuum. We cannot hear the sound of the alarm
clock because it is in a vacuum and there is no air for it to travel in.
Sound can travel in solids, liquids and gases.
Sound travels fastest in solids and slowest gases.
Approximate speed of sound in air is 330m/s and approximate speed of
sound in water is 1500m/s

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Program Stream AG #1 Physics IGCSE 2020

Describe an experiment to determine the speed of sound in air
You need a quiet open space at least 100 m long to perform this investigation.

1. When you see the cymbals crash, press START.
2. When you hear the cymbals crash, press STOP.
3. The speed of sound = distance/time

Relate the loudness and pitch of sound waves to amplitude and frequency

quiet sound loud sound

 The loud sound has taller waves.
 The louder the sound, the greater the amplitude

low pitch sound high pitch sound

 The high pitch sound has a shorter wavelength, so more waves are visible. It has
higher frequency waves.

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Program Stream AG #1 Physics IGCSE 2020

Describe how the reflection of sound may produce an echo
The sound wave is reflected
back from the surface.
What type of sound does this
produce?
echo

Example 1

Reflection of sound off a hard flat surface

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Program Stream AG #1 Physics IGCSE 2020

s = d/t
t= d/s
t= 12.9/ 1500 = 0.0086s

150m

Example 2

The first sound comes from the bell and the second sound comes from the echo off the
steep mountain.

The first sound is the loudest because it did not lose energy by travelling to the mountain
and back as well as being absorb by the mountain.

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Program Stream AG #1 Physics IGCSE 2020

s = d/t
t = d/s
t = 990/330 = 3 s

To the student – 3s
To the mountain -3s
Back to the student for the second time – 3s
Total time = 9 s

iii. A ship blows its horn towards a cliff. An echo is heard 4s later. If the speed of sound in air
is 330m/s, calculate the distance of the ship and the cliff.
Actual time = 4/2= 2s
s = d/t
d=sxt
d = 330 x 2 = 660m

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Program Stream AG #1 Physics IGCSE 2020

Magnetism
 State the properties of magnets
• Give an account of induced magnetism

S N P has to be south because it
is attracted to the north of
the magnet.
If P is south then Q is north.

• Distinguish between ferrous and non-ferrous materials
Ferrous materials has a lot of iron whilst non-ferrous materials do not have a lot of
iron.
Eg. Steel is ferrous because it contains iron and it is magnetic.

Cobalt is non-ferrous because it does not contain iron. It is magnetic

 Iron, steel, nickel and cobalt are magnetic
• Describe methods of magnetisation and of demagnetisation

Magnetisation Demagnetisation
Place magnet into coil and pass a very high Heat the magnet
current
Apply a magnetic field to a molten alloy and Place magnet in a coil with AC voltage and
allow it to solidify remove it from the coil slowly
Hammering steel in a N-S direction Hammering or dropping the magnet

Magnetic field moves from N-S
Iron is a temporary magnet (used in
electromagnets) and steel is a permanent
magnet

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Program Stream AG #1 Physics IGCSE 2020

Electrostatics charged.
When a cloth and the insulator are rubbed

Electrons move from the insulator to the cloth

The cloth becomes negatively charged.

The insulator becomes positively

Positive and positive repel

Negative and negative attract

Positive and negative attract

State that unlike charges attract and that like charges repel

• Distinguish between electrical conductors and insulators and give typical examples
Conductors have free electrons that moves during conduction whilst insulators have no free
electrons and cannot conduct

Inducing a temporary charge
If you bring a negatively charged rod near a piece of paper, why does the paper stick to the
rod?
The paper has no charge!

As the rod approaches the paper, the electrons in the paper are repelled away from
the rod.
This makes one side of the paper negative and one side positive, a charge has been
induced on the paper and the positive side of the paper is attracted to the negative
rod.

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Example 1 Program Stream AG #1 Physics IGCSE 2020

conductor
Copper, iron

Apply voltage/pd
across it

insulator
Wood, plastic
The insulator

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Program Stream AG #1 Physics IGCSE 2020

Electricity

Circuit symbols

Current(I)

Current is the rate of flow of charge. It is measured in amperes (A).
An ammeter is used to measure current. It is connected in series because it has a very low
resistance.

The current is the same in a
series circuit. It moves from the
positive terminal of the cell and
flows to the negative terminal.

Current splits in a parallel circuit. The
sum of the currents in the branches of a
parallel circuit is the equal to the current
that leaves the cell or battery.

A1 = A2 + A3 =A4
Example 2

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Program Stream AG #1 Physics IGCSE 2020

ans

Charge = Current x time

Q=It

Charge measured in Coulombs (C)

Current measured in Amps (A)

Time measured in seconds (s)

Example 3

A current of 6A flows for 3 minutes. How much charge flows?

Q = It

= 6A x (3x60)s Always convert time to seconds!!!

= 1080 C

Electro-motive force

The e.m.f. of a source(power supply or battery) of electrical energy
is measured in volts. E.m.f. is defined as energy supplied by a
source in driving charge round a complete circuit

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Program Stream AG #1 Physics IGCSE 2020

Potential difference(V)

The potential difference or voltage is measured using a voltmeter. Its
unit is volts(V). The voltmeter is connected in parallel because it has
a very high resistance.

For a series circuit, the sum of the voltages for each
component is equal to the voltage across the cell or
battery.

V1 = V2 + V3

For a parallel circuit, the voltage across
the cell/battery is the same as the
voltage across each branch.
V1 = V2 = V3

Example 4

Answer

Example 5

Ans

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Program Stream AG #1 Physics IGCSE 2020

Resistance

Potential difference (V) = current (A) x resistance ()

V = IR

Example 6
A 3 resistor has a current of 3A flowing through it. What is the potential difference across
the resistor?

V = IR
= 3 x 3A

=9V

Longer wires have higher resistance then shorter
ones.
Eg. A 1m wire has 1 Ω resistance therefore a 2m
wire should have 2 Ω resistance

Thicker wires have less resistance then thinner wires. This means the greater the
cross-sectional area of a conductor the less the resistance.
If you double the cross-sectional area of a wire you will half its resistance.

Electrical energy

• Recall and use the equations

P =VI and W = VIt or E =VIt

Example 7

If you have a filament bulb and it has a

potential difference of 200V across it

and a current of 0.2A running through it.

a. At what power is the bulb operating

at? b. How much energy is used up in

2 minutes?

a. P = IV

P = 0.2A x 200V

P= 40W

b. W = VIt
= 200V x 0.2A x (2 x 60)
= 4800J

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Program Stream AG #1 Physics IGCSE 2020

Resistors in Series

Resistors in Parallel

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Program Stream AG #1 Physics IGCSE 2020

Example 8

DC

A
A

Vary the resistance of the voltmeter 5 times and take the
readings of the ammeter and the voltmeter

V3Ω=I R= 0.50A x 3Ω =1.5 V
Vunknown= 6 V – 1.5 V = 4.5V
Runknown= V/I= 4.5V/0.5A=9 Ω

Q = It
= 0.5A x 120 = 60C

P=V x I
= 1.5 V x 0.5 A = 0.75W

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Program Stream AG #1 Physics IGCSE 2020

ans
R = 2Ω

R=2Ω+2Ω=4Ω

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Program Stream AG #1 Physics IGCSE 2020

R = 2Ω x2 Ω
2Ω +2 Ω

Ans = 1 Ω

Ans

Increases
Increases

4.3 (c) Action and use of circuit components

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Program Stream AG #1 Physics IGCSE 2020

Potentiometer

• Describe the action of a variable potential divider (potentiometer)

AB C

0V 3V 6V

At C the variable resistance is very high. The variable resistance has 6V. The motor
moves very slow. At B the resistance is medium. The variable resistance has a p.d. of
3V. The motors speed is only half. When the variable resistor is set to A its
resistance is low. It has 0V and the motor has 6V of p.d. the motor moves very fast.

• Describe the action of thermistors

As temperature increases, the resistance of the thermistor decreases and the current
increases.

resistance R1 is a thermistor. As the temperature increases the

As of R1 decreases. The voltage
V1 V1 decreases and V2 increases.
the temperature decreases the resistance of R1 increases.
increases and V2 decreases.

Remember…. Large R means Large V and Small I

 Describe the action of light dependent resistors
 As brightness increases, the resistance of the LDR decreases and the current

increases.

R1 is a Light Dependant Resistor(LDR). As the brightness
increases the resistance of R1 decreases. The voltage V1
decreases and V2 increases.
As the brightness decreases the resistance of R1
increases. V1 increases and V2 decreases.

Remember…. Large R means Large V and Small I

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Program Stream AG #1 Physics IGCSE 2020

Forward bias

off

Stop- reverse bias

The light will not come on. The diode points in the opposite direction of the current flow.
It is connected in reverse bias. There is no current flow.

Diodes allow current to flow in one direction.
It acts as a rectifier. It changes AC to DC.

Example 2

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Program Stream AG #1 Physics IGCSE 2020

The diode changes AC to DC.
It cuts the bottom half of the
AC cycle.

Circuit A

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Program Stream AG #1 Physics IGCSE 2020

Explain and use the terms digital and analogue (Extended only)
Logic gates can have only one of two values 0 or 1, low or high.
As the signals can only have one of two values, they are DIGITAL signals.
Analogue signals have a range of values or states.
The outputs for logic gates depend upon the inputs and are shown in a truth table(Extended
only)

LDR
When it gets dark the resistance of the LDR increases. The pd of the LDR
increases and the pd. The high voltage in the LDR provides a high enough base
voltage for the transistor to switch on and turn the light on.

Times of the day
Use a variable resistor in place of R1. This can vary the voltage of the
base there by controlling the switching of the light.

Street lights

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Program Stream AG #1 Physics IGCSE 2020

Example 1

low Low high
low

Low
high

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Program Stream AG #1 Physics IGCSE 2020

Example 2

Connect switches to the door that gives a high input(on) when the door not
closed properly. An Or gate must be connected to the system so that when
either input is high the output is high. The output is connected to the alarm

Example 3
6V
0V

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Program Stream AG #1 Physics IGCSE 2020

The resistance decreases

High- Low V and R in the LDR… V in R is high.. A is high
Low - high V and R in the LDR… V in R is low. A is low
High…P connected to +6V part of the cct
Low…Q connected to 0 V part of the cct

AND gate
transistor

When the dark room is in use the switch is on P( +6V). So B is High(1).
When there is light R abd V of the LDR is low and V in resistor R is high. A is
high(1). 1 AND 1is 1. The alarm will come on…….The circuit works

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Electromagnetism Program Stream AG #1 Physics IGCSE 2020

Magnetic field lines into page
out of page
moves from N to S

Circular field around a straight current compass needle moves when
carrying conductor. circuit is switched off or on. This
proves that there is a magnetic
field around a current carrying
conductor.

A solenoid produces a field pattern
similar to a bar magnet.

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Program Stream AG #1 Physics IGCSE 2020

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Program Stream AG #1 Physics IGCSE 2020

ELECTRIC MOTORS

FORCE ON A CURRENT CARRYING CONDUCTOR

A force is experience when a current carrying
conductor is placed in a magnetic field. This
happens because the magnetic field around
the current carrying conductor interacts
with the magnetic field of the magnets to
produce a force.

To find the direction of the force we use Fleming’s left hand motor rule.
Check whether you can find the force on the current carrying wire by using Fleming’s
Left hand rule.
Remember – Father, Mother, Child

THE SIMPLE ELECTRIC MOTOR

A split ring or commutator is attached to the
motor to ensure flows in one constant direction
thereby allowing one side to up and the othe
side to be down so that the motor turns
continuosly.

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Program Stream AG #1 Physics IGCSE 2020

Electromagnetic Induction

When the wire moved between points 3-4
and 5-6 , there was no voltage/emf or current
induced.

When the wire moved between points 1-2
, there was voltage/emf and current
induced. This happens because the wire
cuts the magnetic field perpendicularly.

Current only flows when the magnet
moves in the solenoid. Only a
changing magnetic field produces
emf/voltage.

AC current produces a changing
magnetic field

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A SIMPLE ALTERNATOR Program Stream AG #1 Physics IGCSE 2020

A simple alternator cuts the
magnetic field thereby creating an
AC voltage to light up the bulb.
Slip rings provides a direct current
to the bulb.

Transformers

Secondary coil

Primary coil- Iron core-
Always has an AC strengthens the
source electromagnetic
field

The primary coil has an AC source that
produces a changing magnetic field .
This changing field cuts the secondary
coil thereby inducing an emf/voltage on
the secondary coil.

np/ns =Vp/Vs

Vp/Vs = Is/Ip

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Program Stream AG #1 Physics IGCSE 2020

National power grid

The step up transformer increases the voltage and decreases the current and power
in the power lines so that the AC voltage can travel far distances.
The step down transformer decreases the voltage so that the voltage is smaller and
can be used in our homes.
Example 1

ans Brass is not magnetic.
The compass always
points N.

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Example 2 Program Stream AG #1 Physics IGCSE 2020
Ans.
Iron makes a temporary magnet
Example 3 and steel makes a permanent
magnet

N SN S

Use Right Hand Rule- Remember
Ans knuckles to finger tips.

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Program Stream AG #1 Physics IGCSE 2020

Example 4
Ans.

Ans.
Ans.

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Example 5 Program Stream AG #1 Physics IGCSE 2020

Ans. A changing magnetic field
Example 6 creates an alternating current

Store energy in capacitors
To reduce current and power loss so that it can travel long distances

Remember P = V x I…… but V = I x R …so P = I xR x I….
P =I2R

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Program Stream AG #1 Physics IGCSE 2020

Np/Ns =Vp/Vs…… 1200/Ns =1100/32000…..cross multiply….
1100Ns=1200 x 32000……1100Ns =38400000……
Ns=34909

To find Ip …………P=VI….I=P/V……Ip=800000/1100= 727.3A
Vp/Vs=Is/Ip
1100/32000=Is/727.3
Is = 25A

AC voltage in the primary coil creates a changing
magnetic field that cuts the secondary coil. This
induces a secondary voltage.

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Program Stream AG #1 Physics IGCSE 2020

More turns in the secondary coil

Vp/Vs=Is/Ip
24000/400000=Is/12000
Is = 720A

 High voltage implies lower current and power loss.
Lower power loss, less expense.

 Thinner cable required.

Question 7

Force- Fleming’s left
hand rule

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Program Stream AG #1 Physics IGCSE 2020

The magnetic field around the current carrying wire interacts with
the magnetic field of the magnet thereby creating force.

Stays the same Remember, the cross represents
Force the magnetic field going into the
paper. The negative charge
moves opposite to current
direction. Using the Left Hand
Rule, we can find force.

It curves downwards

answer

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Program Stream AG #1 Physics IGCSE 2020

Remember-
current flows
from + to -

The magnetic field around the current carrying wire interacts with
the magnetic field of the magnet thereby creating force.

Into page Kinetic or
electrical mechanical

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Program Stream AG #1 Physics IGCSE 2020

Commutator/
split rings

The commutator/split rings ensures that one side is always
positive and the other side is negative. This will cause a
continuous turning motion

Answer

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Program Stream AG #1 Physics IGCSE 2020

Atomic model

• Describe the structure of an atom in terms of a nucleus and electrons
Ernest Rutherford and his team of scientists performed a famous experiment in Manchester:
They fired some alpha particles at a piece of thin gold foil (only a few atoms thick):
Observations

 Most of the alpha particles went straight through the foil.
 Some alpha particles were deflected through large angles.
 A very few alpha particles were reflected straight back.

• Describe the composition of the nucleus in terms of protons and neutrons
• Use the term proton number Z
• Use the term nucleon number A

Remember: mass number is the
bigger number. It is on top.

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Isotopes Program Stream AG #1 Physics IGCSE 2020

Radioactivity The carbon atoms have the same atomic number
but different mass numbers. They are called
Alpha isotopes.
Beta
Gamma

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Program Stream AG #1 Physics IGCSE 2020

The numbers on the left =
numbers on the right

The numbers on the left =
numbers on the right

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Program Stream AG #1 Physics IGCSE 2020

Half life

The time it takes the count rate from a radioisotope to decrease by 50%.

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Program Stream AG #1 Physics IGCSE 2020

Summary

Example 1

protons
Protons and neutrons
47 107 -47=60

84-82=2
218-214=4

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Program Stream AG #1 Physics IGCSE 2020

80
40

7.5 hours…check graph
Count rate 160/2=80….time =7.5 +7.5 =15 hours
Count rate 80/2=40….time =7.5 +15 =22.5 hours

0
-1
Beta…electron

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Program Stream AG #1 Physics IGCSE 2020

Example 2

Alpha particles are not penetrating enough to go through the box.
Gamma is very penetrating and may not be affected by the boxes
contents.

Barium-139… It has a short half life so that by the time it is
consumed the radioactive particles are destroyed.

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