PHYSICS IGCSE REVISION GUIDE FOR CANDIDATES MRSM AG 2020

2020

Physics IGCSE Revision Guide

Edited by
Mohamad Rizal Bin Mukhtar
Physics Teacher, MRSM Alor Gajah
Credit to:
Mr Ronesh, HAS Private School

Program Stream AG #1 Physics IGCSE 2020

Length and time

Measure and describe how to measure a short interval of time (including the period of
a pendulum)

The pendulum is released from a given height.
The stop watch will be started. Then swings
will be timed. To find the time for one swing
we divide the time by 10. Repeat the
experiment and find the average in order to
avoid human error.

___________________________________________________________________

Speed, velocity and acceleration

• Define speed and calculate speed from

Speed = distance / time

What is the difference between speed and velocity?

Speed is a scalar quantity, it has only a magnitude.
Velocity is a vector quantity, it has a magnitude and a direction

Example 1

A car drives a distance of 1 500 metres in a time of 75 seconds. What is the average speed
of the car for the journey?

Speed = distance
time

Speed = 1 500m
75s

Speed = 20ms-1

Example 2

A car drives a distance of 35m/s in a time of 180 seconds. What is the distance covered
during the journey?

Speed = distance
time

Distance = speed x time
Distance = 35 x 180
= 6 300m

• Demonstrate some understanding that acceleration is related to changing speed

Acceleration = Change in velocity ÷ Time taken
Acceleration is measured in metres per second squared(m/s2)

a= v–u
t

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Program Stream AG #1 Physics IGCSE 2020

Example 1

A bat accelerates from rest to 8m/s in a time of 4s. What is the acceleration of the bat?
a= v–u
t

Acceleration = 8 - 0 m/s2
4

Acceleration = 2m/s2

Example 2

A motorbike accelerates from 20m/s to 36m/s in a time of 0.8s. What is the acceleration of
motorbike?

a= v–u
t

Acceleration = 36 - 20 m/s2
0.8

Acceleration = 20m/s2

 State that the acceleration of free fall for a body near to the Earth is constant.
Acceleration due to gravity is 10m/s-2

• Plot and interpret a speed/time graph or a distance/ time graph

• Recognise from the shape of a speed/time graph when a body is
– at rest
– moving with constant speed
– moving with changing speed

Remember- the gradient of the distance/time graph gives speed

• Calculate the area under a speed/time graph to work out the distance travelled for motion
with constant acceleration

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Program Stream AG #1 Physics IGCSE 2020

Example 2

b.Calculate the acceleration of the car.(Remember- the gradient of the
velocity/time graph gives acceleration)

a= v–u
t

Acceleration= 0-21 m/s2
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Acceleration = - 0.6 m/s2( the negative sign means that the car is decelerating)

• Describe qualitatively the motion of bodies falling in a uniform gravitational field with and without air
resistance (including reference to terminal velocity)

When the skydiver jumps out
of an aeroplane, weight is
only force that acts on him. As
he falls the air resistance
increases and acts upward. At
a certain point the weight and
the air resistance are equal.
The resultant force and
acceleration is zero. A
maximum velocity called
terminal velocity is reached.

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Program Stream AG #1 Physics IGCSE 2020

When the skier skies down slope, a
component of weight is only force that acts on
him. As he falls the air resistance increases
and acts up the slope. At a certain point the
weight and the air resistance are equal. The
resultant force and acceleration is zero. A
maximum velocity called terminal velocity is
reached.

Mass and weight

To convert mass into weight we multiply the mass by 10.
Eg. A mass of 60kg has a weight of 600N

Mass/kg Weight/N
Amount of matter in a substance Force at which earth pulls objects to its
centre
Not a force Is a force
Units:kg Units:N
Stays the same anywhere Changes from place to place
scalar vector

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The equation of density is: Density

Density = mass
volume

Example 1

10 cm

5cm 3cm

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Program Stream AG #1 Physics IGCSE 2020

The above figure shows the readings that are necessary to find the density of a rectangular
block.

a. The volume of the rectangular block is…

V = 10 x 5 x 3 = 150cm3

b. Calculate the density of the stone

Density = mass

volume

Density = 120g
150cm3

= 0.8 g/cm3

Example 2

The above figure shows the readings that are necessary to find the density of a stone.
a. The volume of the stone is…
120 cm3 – 170cm3= 50cm3
b. Calculate the density of the stone
Density = mass
volume
Density = 120g
50cm3
= 2.4 g/cm3

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Program Stream AG #1 Physics IGCSE 2020

Forces

State that a force may produce a change in size and shape of a body

Hooke’s Law

Hooke’s Law states that extension(e) is directly proportional to stretching force(F).

 Why is the graph not straight from A to E?

The spring has reached its limit of proportionality. It does not obey Hooke’s Law
anymore. Force is not directly proportional to extension.
 Write an equation for Hooke’s Law.

F = kx

Force(F) Spring constant(k) extension(x)

Example 1

A spring is stretched 10mm( 0.01 m) by a weight of 10N.

a. Calculate the force constant

F = kx
k = F/x

k = 10N/0.01m
= 1000N/m

b. The weight of an object that causes an extension of 80mm(0.08m)

F1/x1 =F2/x2 = k

10N/0.01m = F2/0.8m

F2 = 1000 x 0.8
= 800N

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Program Stream AG #1 Physics IGCSE 2020

Example 2

a. What is the extension of the spring?
X = 32mm - 20mm = 12mm

b. If the spring obeys Hooke’s Law, what does it tell you about the extension and the load?
Extension(x) is directly proportional to the weight of the load.

c. What would the extension be if there was a 6N load?
F1/x1 =F2/x2 = k

8N/12mm =6/ x2
x2 = 6 x 12
8
x2 = 8mm

d. As the weights are added the spring reaches its elastic limit. How does this affect the
spring?
The spring does not obey Hooke’s Law anymore. The extension is not directly
proportional to the weight of the load.

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Program Stream AG #1 Physics IGCSE 2020

Circular motion

 Describe qualitatively motion in a curved path due to a perpendicular force
During circular motion the centripetal acceleration and the centripetal force acts towards the
centre of the circle. The velocity vector lies tangential to the circle.

Example 1

a. Centripetal force
b. Refer to the diagram

Ball will travel in
this direction

Example 2

The direction is always changing so its velocity
changes

The centripetal force is required to produce a centripetal acceleration

Towards the centre of the circle
Friction of the tyres and the
road

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Program Stream AG #1 Physics IGCSE 2020

 Describe the ways in which a force may change the motion of a
body
In football the player can use the force of his legs and his body
in order to stop the ball, accelerate the ball, decelerate the ball,
change the direction of the ball, and curl the ball like David
Beckam.

 Find the resultant of two or more forces acting along the same line

5000N

1000N

The net force of the car is: 5000N -1000N =4000N to the right
The net force of the car is: 10N +10N- 7N =13N to the right

Turning Effect of forces

The turning effect of a force is called the moment of a force. It depends on the size of
the force and the distance between the force and the pivot.

The moment is large when the force is large or the distance is large.

Moment (Nm) = Force (N) X Perpendicular Distance from Pivot (m

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Program Stream AG #1 Physics IGCSE 2020

Example 1

Moment on the left = F x d = 50000 x 5 =250000Nm
Moment on the right = F x d = 10000 25 =250000Nm
Moments are the same so the crane is balanced.

Example 2

Moment = F x d = 3N x 40cm =120Ncm

Moment = F x d = 2N x 30cm =60Ncm

Moment on the left = Moment on the right
(2N x 30cm)+(Fx20cm) = 3N x 40cm

60Ncm + 20F = 120Ncm
20F =60

F=60/20=3N
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Program Stream AG #1 Physics IGCSE 2020

Moment on the left = Moment on the right
2N x d = 1.2N x 20cm
2d = 24
d = 12cm

 State that, when there is no resultant force and no resultant turning effect, a system is in
Equilibrium

The three diagrams show no
resultant forces and no turning
effect. They are all in equilibrium

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Program Stream AG #1 Physics IGCSE 2020

Centre of Mass

The centre of mass is the point where we assume all the mass of an object is
concentrated.

To find the centre of mass of an irregular
shaped object we hang the object. Suspend a
mass from the same place. Mark the line of the
string on the irregular shaped object. Turn the
object and repeat the procedure. The centre of
mass is where the 2 lines meet.

 Describe qualitatively the effect of the position of the centre of mass on the stability of simple

objects

The cubes are stable because because a
line drawn downwards from the centre of
mass falls on its base. It is stable.

The surfer will fall into the water because a line
drawn downwards from the centre of mass does
not fall on the surfboard but into the water…
“Wipe Out”

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Program Stream AG #1 Physics IGCSE 2020

 Demonstrate an understanding of the difference between scalars and vectors and give

common examples

Example 1

Add vectors by graphical representation to determine a resultant

To find the resultant vector in this case you need to join the staring point to the
finishing point.

5m 6m 4m
start 4m

displacement

finish

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Program Stream AG #1 Physics IGCSE 2020

The total distance of this journey = 5m + 6m + 4m + 4m = 19m
The displacement of the journey is from the starting point to the finishing point
of the journey.

Determine graphically the resultant of two vectors

60˚

5cm

8.66cm Construct vector
diagram.
resultant
50 N = 5cm
8.66cm
86.6N = 8.66cm
5cm
Complete the
parallelogram- check
the grey lines.

60˚- use protractor

Remember: the resultant will be in cm- Multiply the resultant by 10 to convert it into
force. The above diagram is not drawn to scale.

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Program Stream AG #1 Physics IGCSE 2020

Energy

Mass= E

60kg D
A C

5m

B
At point A- the skater has gravitational potential energy
GPE = m g h = 60 x 10 x 5= 3000J

At point E- the gravitational potential energy is converted into kinetic energy as the skater
moves down the slope.

At point B- All the potential energy is converted into kinetic energy
GPE at A = KE at B
m g h = ½ m v2

g h = ½ v2
v2 = 2 g h = 2 x 10 x 5 = 25
v = √25 = 5 m/s

At point C- If the skate track had friction, the energy will be converted into heat and sound.
The skater will stop at point C.

At point D- If the skate track did not have friction the skater will stop at point D.

At point E- the skater never reaches point E due to the principle of the conservation of
energy.
Energy in a system may take on various forms (e.g. kinetic, potential, heat, light). The
law of conservation of energy states that energy may neither be created nor
destroyed but transferred from one form to another.

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Example 1 Program Stream AG #1 Physics IGCSE 2020

Mass of bob = 1kg

B A

0.3m

GPE = mgh
1 x 10 x 0.3 = 3J

GPE at point A= 3J
GPE at point B = m g h = 1 x 10 x (0.3m-0.2m) = 1J
KE = the difference of the potential energy = 3J – 1J= 2J

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Program Stream AG #1 Physics IGCSE 2020

KE = ½ mv2
1J = ½ x 1 x v2
v2 =2

v =√2= 1.4m/s

0.3m

Refer to diagram

 Distinguish between renewable and non-renewable sources of energy

Renewable resources can be can get used up totally whilst non renewable resources can get
used up totally.

The wind turns the blades of a wind mill in order to generate electricity.
The solar cells traps the suns energy and converts it into heat and electricity
Hydroelectric energy is created by moving water that turns the turbines to create electricity
Bio fuels from plants can be used to make ethanol that can be used to replace petrol. Bio
waste can also produce methane. Geothermal heat from the rocks can be used to heat water.

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Program Stream AG #1 Physics IGCSE 2020

Renewable Non-renewable
Wind energy Nuclear fission-Nuclear

Hydro Power energy
Solar Energy Natural gas
Geothermal
Coal
Oil

Work and Power

Example 2

Work = Force x distance
Refer to diagram-
W=Fxr
The answer is C!!!

Power is the rate at which work is done.
Watt(W) is the unit of Power??!!!

P=W/t

Example 3

A crane lifts a steel girder with a mass of 800kg. The girder rises 21m in 6 sec.
a. Calculate the work done
b. What is the power of the crane

a. Work is equal to the energy transferred. W = m g h = 800 x 10 x 21 = 168000J

b. P = W/ t
= 168000/6
= 28 000W

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Program Stream AG #1 Physics IGCSE 2020

Pressure

Pressure is a measure of how spread out a force is over a specific area

If you wish to increase the pressure exerted by a force over an area you can...
a. Increase the size of the force
b. Decrease the area the force is acting over

the Sharpening knives decreases
edge surface area of the cutting
which increases the pressure
exerted by the knife making it
easier to cut through objects

Pressure (Pa) = Force
(N)

Area(m2)

Example 1

An elephant has a weight of 40 000N. Each of its feet covers an area of 125cm2. If
the elephant has all four feet on the ground, what pressure will the elephant put upon
the ground?
Pressure = Force

Area
Total area = 4 x 125cm2 = 500cm2
Pressure = 40 000N

500cm2
Pressure = 80N/cm2

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Program Stream AG #1 Physics IGCSE 2020

Example 2

1. Why do camels have feet with a large area?

Camels are often heavy and can spend a lot of their time on sand and
other soft ground. By having feet with a large surface area in contact
with the ground this decreases the pressure the camel exerts on the
ground making it less likely the camel will sink into sand etc

2. Why do eagles have sharp beaks and talons?

Eagles have sharp beaks and talons because this decreases the surface
area of the cutting edge which increases the pressure exerted by the
beak and claws making it easier to cut through flesh

Liquid Pressure

As you move down the measuring cylinder the water is pushed
out with greater force because for liquids and gases the
pressure increases with depth. This is because the lower down
you are in a liquid or a gas, the greater weight of substance above
there is pushing down on the liquid or gas, hence the greater the
pressure.

Liquid Pressure (Pa) = h (height) x g x d(density)

Hydraulics Piston 2

Piston 1

F1 F2 A small force (F1) exerted by
A1 A2 piston one downwards, which has

(A2). a small area (A1), increases the

pressure (P1) in the fluid and is

multiplied into a large force (F2) by

piston two, which has a large area

P1 = P2 ( The pressure on both sides will be the same)

F1 / A1= F2 / A2

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Program Stream AG #1 Physics IGCSE 2020

Example 4
Refer to the above diagram

If F1 = 5N, A1 = 0.2m2 , A2 = 1.2m2 find F2 = ?

Solution

P1 = P2

F1 / A1= F2 / A2

5/0.2 = F2 /1.2

F2= 30N

Boyle’s Law

For a fixed mass of gas at a fixed temperature the volume is inversely
proportional to the pressure.

Boyles law implies that if you increase pressure then volume will decrease.

P1V1 = P2V2

Example 5

A gas of volume 30cm3 has a pressure of 3kPa, when the same mass of gas is
compressed to 15cm3, what is the new pressure of the gas? Assume the
temperature is constant

P1V1 = P2V2

3000 x 30 = P2 x 15

P2= 6000Pa

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Program Stream AG #1 Physics IGCSE 2020

 Use and describe the use of a manometer
The U-tube manometer is used to measure gas pressure

10cm

10cm

Pgas =Patmos

Gas pressure is greater than atmospheric pressure
Gas pressure = 20cm + atmospheric pressure

10cm 10cm

Gas pressure is less than atmospheric pressure
Gas pressure = atmospheric pressure 20cm

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Program Stream AG #1 Physics IGCSE 2020

 Describe the simple mercury barometer and its use in measuring atmospheric
pressure

The pressure here is 0 because this is a
vacuum

The atmospheric
pressure pushes
the mercury
downwards

This height measures the
atmospheric pressure

Remember- the thicker tube will give the same atmospheric
pressure reading

Example 1

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Program Stream AG #1 Physics IGCSE 2020

answer

Example 2

P = h g d = 2 x 10 x 1000 = 20 000Pa

P = F/A
A=F/P =50/20000

= 0.0025Pa

The gravitational potential energy is converted in kinetic ,
heat and sound energy

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Program Stream AG #1 Physics IGCSE 2020

Example 3

answer

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Program Stream AG #1 Physics IGCSE 2020

Thermal Physics

 State the distinguishing properties of solids, liquids and gases

Kinetic Theory

 The three phases of matter are …solid, liquid and gas
 Matter is made up of tiny particles called atoms and molecules
 These particles are in constant motion.
Solid molecules vibrate
Liquid molecules slide over each other
Gases are in constant random motion

Example 1

Match the following statements with a phase of matter.

1. Particles vibrate in fixed positions solid
2. Particles vibrate but changes position liquid
3. Particles move around at high speeds gas
4. No fixed shape or volume gas
5. Fixed volume but no fixed shape liquid
6. Forces of attraction is weak gas

Extension question
When a perfume is sprayed, why can a person standing some distance away get the
fragrance?

Small fast moving air molecules collide with the large slow moving perfume particles.

Temperature is the measure of the average kinetic energy of molecules.

When gas molecules are heated they gain kinetic energy and move faster.

Example 2

1.a. What do think would happen if a spray can is thrown into a fire? It may explode
1.b. Use the kinetic molecular theory to explain why this happens? The gas molecule in the
can may get hot and move faster. This will cause them to hit the sides of the container
harder and faster. The pressure of the can will increase and explode.

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Program Stream AG #1 Physics IGCSE 2020

1.c. From the above example what do you think is the relationship between pressure and
temperature? The higher the temperature the greater the gas pressure
2. How is pressure in a gas created?

Gas pressure is created when gas molecules hit the walls
of the container it is stored in.

3. What is the effect of pressure in a fixed container if:

a. The gas is cooled decrease
b. The gas is heated increases
c. The gas expands increase
d. The gas is compressed increase

Brownian Motion

Smoke cell experiment-

When observed from a microscope,
brightly coloured specks are seen dancing
randomly. This is caused by small, fast
moving air molecules colliding with large,
slow moving smoke particles.

The lamp and the lens allows us to see the brightly
coloured specks dancing in random motion.

Dust particles- When observed dust particles are seen
moving in random motion. This is caused by small, fast
moving air molecules colliding with large, slow moving
dust particles.

Evaporation occurs when high energy
surface molecules escape from the
liquid. This causes the liquid to lose
energy and cool down. It occurs at any
temperature and is not boiling. It leave
the liquid feeling cooler.

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Program Stream AG #1 Physics IGCSE 2020

Apply perfume/alcohol to your body...
You will feel COOL !
Evaporation is a cooling effect

Wind or draught causes air molecules to collide with the liquids
surface molecules and transfers energy for the liquid molecule to escape.
The higher the temperature the more energy obtained by the surface molecules. The higher
the evaporation.
Try spreading a liquid spill. This increases the surface area of the liquid and evaporation
increases.
The higher the humidity the lower the evaporation

 Evaporation occurs at all temperatures. It occurs when
1) the temperature is high- more evaporation
2) The surface area is large- more evaporation
3) The wind or draught is blowing over the surface of the water- more evaporation

Evaporation Boiling
Occurs at any
temperature Occurs at a definite
temperature — the
Occurs at surface
No bubbles formed boiling point
Occurs within liquid

Bubbles appear

Example 3

Why do people wrap a bottle containing milk with a damp cloth?

The more energetic surface molecules of the liquid escape from the damp cloth taken
away some energy with it. This causes the cloth to cool thereby cooling the milk.

Expansion

Solids

Example 4

 Why are there expansion gaps in roads and bridges ? Use the concept of
contraction, expansion and the kinetic molecular theory in your answer.

During hot days the bridge expands due to the heat energy given to its molecules.
The expansion gaps actually prevents the bridge from collapsing due to the
expansion.

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Program Stream AG #1 Physics IGCSE 2020

 Explain how axles can fit into gear wheels but it is so difficult to move it apart.
Liquid nitrogen cools the big axle causing the molecules to loose heat energy.
This causes the axle to shrink and it fits into the smaller wheel. The axle than
is allowed to heat up and expands and the axle and wheel locks.

Bimetallic strips

Example 5

 How many metals does a bimetallic strip have? 2
 Which metal expands first, copper or iron? copper
 When expansion occurs in this case what happens? Bends away from copper

Example 6

How are bimetallic strips used in the following instances?

a) fire alarm

b) thermostat

Alarm or
heater circuit

copper

iron

a. fire alarms The circuit of the alarm is broken. In an event of a fire the bimetallic
strip gets hot and completes the circuit. When this happens the strip bends away
from the copper and switches the siren on

b. thermostat The circuit of the thermostat is complete and when a certain
temperature is reached the strip bends away from the copper strip and breaks the
cct. allowing the device to cool.

Expansion of liquids

At 0C water freezes and expand. This is due to the spaces between it
hydrogen bonded molecules

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Program Stream AG #1 Physics IGCSE 2020

Example 7

Explain why fish can survive in a frozen lake?

Due to the molecular arrangements of the hydrogen bonds of water it actually
expands when it freezes. Water reaches its maximum density when it reaches
4C. In the lake the dense water that is 4C sinks to the bottom and the water
on the top freezes and drop to low temperatures. The fishes survive in the
bottom where the water is warmer.

Thermometers

boiling point - Temperature at which a liquid turns into gas without any increase or
decrease in temperature.
melting point- Temperature at which a solid turns into liquid without any increase or
decrease in temperature.
 What is temperature? Measure of the average kinetic energy of the molecule

Liquid-in-glass thermometer
 What happens to a liquid when it is heated?
It expands
 This principle is used in a liquid-in-glass thermometer

Upper fixed point

Lower fixed point

capillary

1) The liquid expands rapidly by the change in temperature over a wide range.
2) Mercury or coloured alcohol is used as the liquid.

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BOILING POINT MERCURY Program Stream AG #1 Physics IGCSE 2020
MELTING POINT 357C
-39C ALCOHOL
78C
-115C

 Which liquid would you use to measure low temperatures? Explain
Alcohol, takes a very low temperature to freeze.

 Which liquid would you use to measure high temperatures? Explain
Mercury, it has a very high boiling point

Define lower fixed point and upper fixed point
lower fixed- freezing point of pure water
upper fixed- boiling point of water

 How are the points found?

lower fixed- freezing point of pure water is reached and the thermometer is placed on
the water and the mercury rise is marked.
upper fixed- boiling point of pure water is reached and the thermometer is placed on
the water and the mercury rise is marked.

 How would you calibrate a thermometer?
Dividing the upper and lower fixed point into 100

Sensitivity, Range and Linearity

Sensitivity- When a thermometer gives a large response to a small change in temperature.
A Thermometer can be made sensitive by having a large bulb and a very narrow tube.

Range- The values within the highest and lowest temperature that a thermometer can
measure.

Linearity- The markings between the upper fixed point and the lower fixed point is increased
by the same amount.

Accuracy – An accurate thermometer gives the correct values of temperature. This is
different form sensitivity.

Thermocouple thermometer

You are required to draw a labelled diagram of a thermocouple thermometer.

A difference in temperature between the hot junction and cold junction causes a
voltage to be produced. The sensitive voltmeter gives a reading. The voltmeter is
calibrated to read temperature.

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Program Stream AG #1 Physics IGCSE 2020

 Used to measure temperature in hard to
reach places such as cracks in walls and
volcanoes.

 Large range of temperature to be measured
 When there is a small temperature change
 To measure very high temperature

Thermal Capacity

When a match burns its internal energy increases

Specific heat capacity

If 1kg of water and 1 kg of aluminium was heated for the same time which would have a
higher temperature rise?
Water is greedy. It needs 5 times as much temperature rise to produce the same
energy. So aluminium will have the higher temperature rise.
4200J of energy is required to raise the temperature of 1kg water to 1C. 4200 J is
called the specific heat capacity.
Specific heat capacity of a substance is the energy required to raise the temperature
of 1kg of substance by 1C

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Program Stream AG #1 Physics IGCSE 2020

 To calculate the amount of energy needed we use the following equation

Example SHC

Why does the inside of a pie get hotter than the outside after it has been heated in a
microwave oven?
The specific heat capacity of the outside of the pie is greater than the specific heat
capacity of the inside of the pie. The higher the specific heat capacity the longer it
takes to heat up.
What does 8 kW means?
This is the power rating. I means that 8000J of energy is given out every second.
A tank holding 60kg of water is heated by a 3kW heater. If the specific heat capacity of
water is 4200J/kgC, Estimate the time taken for the temperature to rise from 10C to 60C.
First we need to find the energy needed:
Q = m c ∆T

= 60 kg x 4200 x (60-10)
= 12600000J
To find the time we use the power equation:
P = W/t
t = W/P
t= 12600000/3000 = 42000 s

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Program Stream AG #1 Physics IGCSE 2020

Specific Latent Heat

What happens when you melt 1kg of ice completely?
To melt 1kg of ice at we must provide 340 000 J of energy.

During the process of melting the temperature of the water stays the same, it does not
get warmer. The energy provided is called hidden heat or latent heat. The number
340000J is called the specific latent heat of fusion for water. Fusion means melting.
The specific latent heat of fusion is the energy required to melt 1kg of substance
without changing its temperature (lf).

Example Melting

Why are ice cubes used to cool down drinks?
During the meting process of ice, the ice removes heat energy from the cool drink.
The ice melts without its temperature changing at 0 C. This causes the drink to
remain cool.
The equation used to find the energy for melting is:

Q = mlf

Vaporisation

 What happens when water is heated to 100C?

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Program Stream AG #1 Physics IGCSE 2020

The latent heat is used to overcome the forces between the molecule and water is
changed into steam. To boil 1 kg of water into steam at 100C we must provide a
latent heat of 2300000J. This number is called the Latent heat of vaporisation. Notice
that the temperature does not change.
The latent heat of vaporisation Is the energy required to boil 1 kg of a substance into
gas without changing its temperature.
The equation used to find the energy for boiling/vaporisation is:

Q = mlv

Example Boiling

Explain why the latent heat of vaporisation of water is greater than latent heat of fusion of
ice.
The liquid molecules need a lot of energy to overcome the forces holding them
together to become a gas. Latent heat of vaporisation is required increase kinetic
energy and expansion of the gas molecules. This requires a lot of energy.

Example

Calculate the quantity of heat required to convert 5 kg of ice at -7C to
Water vapour at 100C.

cice ( SHC of ice)= 2100J/Kg.C
cwater (SHC of water )= 4200J/Kg.C
lf ice ( laten heat of fusion)= 336J/kg
Lv water(Latent heat of vaporisation)2273J/kg
What changes must ice go through to become water vapour?

T (C)

time(s)

 You are required to use the above graph to show when boiling,
melting and temperature change takes place. Notice that during melting and
boiling the temperature stays constant.

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Program Stream AG #1 Physics IGCSE 2020

Q = mc∆T ( energy that doesn’t require change in phase)

Q = ml ( energy that require change in phase)

step1 Q = mc∆T (raising heat from 7C t0 0C)

= 5 x 2100x 7

= 73500J

step2 Q = mlf (melting phase)
= 5 x 336

= 1680J

step3 Q = mc∆T (raising heat from 0C t0 100C)

= 5 x 4200x 100
= 2100000J

step4 Q = mlv (boiling or vaporisation phase)

= 5 x 2273

= 11365J

Total energy required is equal to = 73500J + 1680J +2100000J + 11365J = 2186545J

You must go over the details of the experiment and the worked
examples

(Describe an experiment to measure specific latent heats for steam and for ice and specific
heat capacity of a solid block)

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Program Stream AG #1 Physics IGCSE 2020

Example 1

Q = mlv
VIt = (m1 – m2) lf
Lf= VIt/(m1 – m2)

Lf= VIt/(m1 – m2)
= 12V x 2Ax 3750/40g

= 2250J/kg

The liquid molecules need a lot of energy to overcome the forces holding
them together so that they can become a gas. Latent heat of vaporisation is
required increase kinetic energy and expansion of the gas molecules. This
requires a lot of energy.

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Program Stream AG #1 Physics IGCSE 2020

Example 2

Refer to graph

Boiling point has been reached. During boiling the temperature stays the same
100°C

The energy is used to break the bonds that are holding the water in liquid
form so that it can become a gas and the energy is required to push the gas
molecules apart.

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Program Stream AG #1 Physics IGCSE 2020

Example 3

Internal energy

Aluminium has a higher Specific capacity than
copper so aluminium’s temperature rise is less

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Program Stream AG #1 Physics IGCSE 2020

Transfer of thermal energy

 Heat is transferred by Conduction , Convection and Radiation

Condution

 Copper is the
best conductor
of heat

 Heat is
transferred through
the rod and melts
the Vaseline. The
nails will fall

During heat conduction of a metal the heat travels fom hot to cold.
WHEN A METAL IS HEATED
THE MOLECULES
VIBRATE FASTER.

 THEY COLLIDE
WITH THE
NEIGHBOURING
MOLECULES
TRANSFERING
HEAT

Convection

Convection takes place in gas and liquids.
The hot fluid gets less dense and rises. When
it is cooled it gets more dense and falls. The
cycle repeats itself.

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Program Stream AG #1 Physics IGCSE 2020

Radiation

Radiation from the electromagnetic spectrum such as infrared, radio waves etc travels as
fast as the speed of light. It does not need a medium to travel. An example is the way we get
heat from the sun.
WHICH MATERIALS ARE GOOD EMITTERS?

 Dark matted surfaces are good emitter whilst light shiny surfaces are poor
emitters.

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Leslie cube Program Stream AG #1 Physics IGCSE 2020

Haa Ha 5.c. Fill a Leslie cube with hot water. Place
the temperature sensor the same distance
from the different surfaces. Record the
temperature and compare

radiometer

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Program Stream AG #1 Physics IGCSE 2020

Waves

Mechanical Waves
The two types of waves are longitudinal and transverse.
You are required to know how to identify and label both sets of waves. Sound
waves are the only longitudinal waves that we study.

wavelength

Waves transports energy from one point to another
In transverse waves the particle vibrate 90° to the wave motion.

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Program Stream AG #1 Physics IGCSE 2020

Longitudinal waves the particle vibrate parallel to the wave motion.

Key Points

 Wavelength is the distance between
2 consecutive points in phase.

 one oscillation is equal to wavelength
 the time take for one oscillation is

called Period.
 Frequency is the number of waves

passing a point in 1 second
 A frequency of 250Hz means that

250 waves passes a point in 1
second.

Recall and use v = f x λ.

Example 1

Eg. Hi FM is broadcasted on radio frequency of 94.5 kHz. What is its
wavelength?

You should realise that Radio waves travel as fast as the speed of light (
3 x 108 m/s)

v=fxλ
λ=v/f

= 3 x 108 m/s
94500Hz

= 3175m

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 Find the number of Program Stream AG #1 Physics IGCSE 2020
waves shown. 3
A
 What is the amplitude λ
A?
The law of reflection states that the :
 Find the wavelength λ. Angle i = angle r
(Use a ruler)

Reflection

Example 2

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Program Stream AG #1 Physics IGCSE 2020

Refraction

Do you notice that the wavelength of the water
waves decreases as the wave reaches the
shallow shore line. This implies that the water
waves will slow down in shallow water.

The water waves tends to bend as it moves
from deep to shallow water.

The wave length decreases as the water bends from deep
to shallow.

From v = f x λ

If λ decreases then the velocity decreases because
frequency is constant.

Example 3

The wave length decreases as the water bends from deep to
shallow.
From v = f x λ
If λ decreases then the velocity decreases because frequency is
constant.

Diffraction

Diffraction of waves occurs when the wave passes an
edge or a gap. Can you notice that there is a larger
diffraction when the gap is smaller? The wavelength
does not change.

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Program Stream AG #1 Physics IGCSE 2020

Example 4

When drawing the diffraction pattern
you must draw at least 3 wavefronts.
Also ensure that the distance between
the waves are equal the wavelengths
and are the same.

v=fxλ
f=v/ λ
= 20c m/s

2.5cm
f = 8Hz

f = 8Hz

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Program Stream AG #1 Physics IGCSE 2020

Light

Reflection of light

The law of reflection states that the :
Angle i = angle r

Mirrors work on the principle of reflection. Images in the mirror are
always:

Virtual
Laterally inverted
Same size as the object
Same distance behind the mirror as
The object is in front

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Example 1 Program Stream AG #1 Physics IGCSE 2020

X She can see till
this point

She cannot see
below this point

Refraction
Refraction causes bending and change in speed of light

The light ray slows down in glass and bends towards
the normal.
It speeds up in air and bends away from the normal.

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