PAL (IGCSE) – PHYSICS
Section 2 Thermal Physics
Thermal Physics
PAL (IGCSE) Single Science
Revision Book - Section 2
Name:
_________________________________
Teacher:
_________________________________
DIPONT Educational Resource – Science
1
PAL (IGCSE) – PHYSICS
Section 2 Thermal Physics
Syllabus Content_______________________________
DIPONT Educational Resource – Science
2
PAL (IGCSE) – PHYSICS
Section 2 Thermal Physics
DIPONT Educational Resource – Science
3
PAL (IGCSE) – PHYSICS
Section 2 Thermal Physics
Syllabus Details________________________________
2.1 Simple kinetic molecular model of matter
2.1 (a) States of matter
Core
• State the distinguishing properties of solids, liquids and gases
2.1 (b) Molecular model
Core
• Describe qualitatively the molecular structure of solids, liquids and gases
Gas
Liquid
Solid
Increasing Kinetic Energy
• Fixed volume
• Fixed shape
• Molecules held in position
by strong bonds
• Molecules vibrate about
fixed position
• Higher temp = higher
vibrations
• Fixed volume
• Shape of container
• Molecules can vibrate and
move but are held close
together by strong bonds
• Expands to fill container
• Molecules can vibrate and
move around freely
• Only very weak bonds exist
between molecule
• Interpret the temperature of a gas in terms of the motion of its molecules
INCREASING
TEMPERATURE
As temperature increases the particles move faster
DIPONT Educational Resource – Science
4
PAL (IGCSE) – PHYSICS
Section 2 Thermal Physics
• Describe qualitatively the pressure of a gas in terms of the motion of its molecules
Pressure in gases
• Molecule collides with wall
• Momentum changes
• Force on molecule from wall
• Equal and opposite force on wall
from molecule
• This averages over time to a
constant force on the wall
• The force per unit area of the
wall is the pressure
Force on
molecule
Force on wall
• Describe qualitatively the effect of a change of temperature on the pressure of a gas at
constant volume
Pressure / Pa
Constant volume
P/T = constant
P1 /T1 = P2 /T2
Temperature / K
Increasing
Temp
At a constant volume the pressure
of a gas is proportional to its
temperature in Kelvin.
DIPONT Educational Resource – Science
AS THE TEMPERATURE INCREASES
• The molecules have more kinetic Energy
• Faster moving molecules will hit the walls with
more force
• Faster moving molecules will hit the walls more
often
• The total force on the walls will increase
• The pressure will increase
5
PAL (IGCSE) – PHYSICS
Section 2 Thermal Physics
• Show an understanding of the random motion of particles in a suspension as evidence for
the kinetic molecular model of matter
• Describe this motion (sometimes known as Brownian motion) in terms of random molecular
Bombardment
Smoke (oil droplets)
Brownian Motion
Path of one droplet



Smoke (oil droplets) are seen to move randomly
This motion is evidence that the air particles are also moving randomly and
colliding with the smoke droplets
The air particles cannot be seen but their motion can be understood by the
smoke droplets which can be seen
Supplement
• Relate the properties of solids, liquids and gases to the forces and distances between
molecules and to the motion of the molecules
Property
Solid
Liquid
Gas
Forces between
particles
Distances between
particles
Motion of particles
Strong bonds
(strong forces)
Fixed and short
Strong bonds
(strong forces)
Short but not fixed
Essentially no bonding
(v-weak forces)
Long
Vibrating only
Vibrating and freely
moving
Vibrating and freely
moving
• Show an appreciation that massive particles may be moved by light, fast-moving molecules
• Small fast moving particles collide with larger particles
• The smaller particles momentum changes and exert a force on the larger
particles
• The larger particles motion changes as a result of these collisions
DIPONT Educational Resource – Science
6
PAL (IGCSE) – PHYSICS
Section 2 Thermal Physics
2.1 (c) Evaporation
Number
Core
• Describe evaporation in terms of the escape of more-energetic molecules from the surface
of a liquid
• Relate evaporation to the consequent cooling
Enough energy
to Evaporate
Energy
A. At all temperatures there will be a distribution of kinetic
energy within the liquid.
B. Molecules with high kinetic energy can ‘escape’ the
liquid and become a gas: Evaporation.
C. The average speed of the molecules in the liquid will
decrease: Therefore, the temperature of the liquid will
decrease.
Supplement
• Demonstrate an understanding of how temperature, surface area and draught over a
surface influence evaporation
Factor
Influence
Temperature
Increases evaporation as more particles have
sufficient kinetic energy to “escape” the
surface
Increases evaporation as “removes” high KE
particles from above the surface of the liquid
Increases evaporation as more surface for
particles to “escape” from
Draught
Surface area
DIPONT Educational Resource – Science
7
PAL (IGCSE) – PHYSICS
Section 2 Thermal Physics
2.1 (d) Pressure changes
Core
• Relate the change in volume of a gas to change in pressure applied to the gas at constant
temperature
Supplement
• Recall and use the equation pV = constant at constant temperature
Pressure / Pa
Constant Temperature
PV = constant
P1 V1 = P2 V2
1/Volume / m-3
Decreasing
Volume
AS THE VOLUME DECREASES
• The distance between each collision with the wall
decreases
•Each molecule will collide with the walls more
often
• The average force against the walls will increase
• The pressure will increase
At a constant temperature the
pressure of a gas is inversely
proportional to its volume.
2.2 Thermal properties
2.2 (a) Thermal expansion of solids, liquids and gases
Core
• Describe qualitatively the thermal expansion of solids, liquids and gases
Solids


As the temperature increases the bonds in the solid vibrate more
The average separation between particles increases and so the bulk
solid expands
The forces between
the atoms and
molecules are similar
to those of a spring
Bond under tension
Bonds ‘pull’ atoms back to original position
Bond under compression
Bonds ‘push’ atoms back to original position
DIPONT Educational Resource – Science
8
PAL (IGCSE) – PHYSICS
Section 2 Thermal Physics
Liquids


As the temperature increases the motion of the particles increase and
so the kinetic energy
The average separation between the particles increases so the volume
of the bulk liquid increases
Gases
 The volume / dimensions of a gas are fixed by the container
 As the temperature increases the motion of the particles increase and
so the kinetic energy
 The particles will collide with the container with more force and more
often
 If the container dimensions are free to change the volume will increase
• Identify and explain some of the everyday applications and consequences of thermal
expansion
State
Application
Consequence
Solid
Railway lines
Liquid
Jam jar lids
In thermometers
Gas
Car tyres
Railway lines to space to expand at the
end of the line
If heated can be removed more easily
As the liquid expands on heating this
property can be used to measure
temperature
After a long journey the pressure in your
car tyres will increase as they become hot
when driving
• Describe qualitatively the effect of a change of temperature on the volume of a gas at
constant pressure
Volume / m3
Constant Pressure
V/T = constant
V1 /T1 = V2 /T2
Temperature / K
Increasing
Temp
At a constant pressure the volume
of a gas is proportional to its
temperature in Kelvin.
DIPONT Educational Resource – Science
• As Temperature increases molecules have more
kinetic Energy
• Faster moving molecules will hit the walls with
more force pushing the walls out
• The volume will increase (if pressure remains
constant)
9
PAL (IGCSE) – PHYSICS
Section 2 Thermal Physics
Supplement
• Show an appreciation of the relative order of magnitude of the expansion of solids, liquids
and gases
State
Order of magnitude of expansion
Solid
Liquid
Gas
Small
Small
Big
2.2 (b) Measurement of temperature
Core
• Appreciate how a physical property that varies with temperature may be used for the
measurement of temperature, and state examples of such properties
Physics property
Volume of a liquid
Effect of temperature
Increases with increasing
temperature
Increases with temperature
Resistance
Example
Mercury in glass
thermometer
Resistance thermometer
• Recognise the need for and identify fixed points
Fixed Points:
 Used to calibrate thermometers
 Boiling and melting water can be used as these 2 changes occur at fixed
temperatures
 The thermometer can be placed in boiling water to make the 100oC mark and
then ice to make the 0oC mark
• Describe the structure and action of liquid-in-glass thermometers
High Temp
Low Temp
• As temperature rises liquid expands
• At any temperature the liquid will have a
fixed volume
Liquid
DIPONT Educational Resource – Science
10
PAL (IGCSE) – PHYSICS
Section 2 Thermal Physics
Supplement
• Demonstrate understanding of sensitivity, range and linearity
Sensitive
Not
Sensitive
Low Range
100oC
500oC
100oC
Non Linear
Range
Linear
Range
High Range
500oC
100oC
50oC
10oC
0o C
0o C
0oC
0o C
• Describe the structure of a thermocouple and show understanding of its use for measuring
high temperatures and those that vary rapidly
V
Thermocouple
thermometer
Copper wires
Iron wire
Hot
junction
Cold
junction
Thermocouple Thermometer
 Consists of two metals connected as shown
 When one junction between the two metal types is at a higher temperature
than the other a voltage is produced
 This voltage is dependent on the temperature difference between the
junctions
 They have a very large temperature range and can record temperatures very
quickly
2.2 (c) Thermal capacity
Core
• Relate a rise in the temperature of a body to an increase in internal energy
Internal Energy = Random Kinetic Energy + Potential Energy of the particles


If temperature rises this indicates that the Kinetic energy of the particles has
increased
If the kinetic energy of the particles increases so does the internal energy
DIPONT Educational Resource – Science
11
PAL (IGCSE) – PHYSICS
Section 2 Thermal Physics
• Show an understanding of the term thermal capacity
Thermal Capacity
The energy required to raise the temperature of an object by 1K
C=
DQ
DT
(J /K)
DQ = change in energy
DT = change in temperature
Specific Heat Capacity
The energy required to raise a unit mass of a substance 1K
c=
DQ
mDT
(J /kgK)
Supplement
• Describe an experiment to measure the specific heat capacity of a substance
Heater
Object
V
c=
A



ItV
m(T2-T1)
Measure the temperature of a material before and after heating
Measure the energy input from heating by measuring the voltage,
current and time
Remember that the block should be insulated as energy will be lost to
the surroundings
DIPONT Educational Resource – Science
12
PAL (IGCSE) – PHYSICS
Section 2 Thermal Physics
2.2 (d) Melting and boiling
PHASE CHANGE
Temperature
Core
• Describe melting and boiling in terms of energy input without a change in temperature
Boiling
PHASE CHANGE
Condensing
Melting
solidification
SOLID
GAS
LIQUID
Time
• State the meaning of melting point and boiling point
Melting point: The temperature at which solid and liquid phases both exist in equilibrium
Boiling point: The temperature at which a substance changes from a liquid to a gas
throughout the bulk of the liquid
• Describe condensation and solidification
Condensation: As the kinetic energy of particles decreases the attractive forces between
them “pull” them together into droplets. Bonds are formed.
Solidification: As the kinetic energy of particles decreases permanent bonds form between
the particles so they are no longer able to move freely.
Supplement
• Distinguish between boiling and evaporation
Property
Boiling
Evaporation
Temperature
Location
Particles
Only at the boiling point
Throughout the liquid
All particles
Temperature of liquid
Remains the same
At all temperatures
Only at the surface
Only the particles with
sufficient kinetic energy
Reduces
• Use the terms latent heat of vaporisation and latent heat of fusion and give a molecular
interpretation of latent heat
LATENT HEAT OF VAPORISATION:
Energy change associated with a substance
Boiling or Condensing
LATENT HEAT OF FUSION:
Energy change associated with a substance
Melting or Solidifying
DIPONT Educational Resource – Science
13
PAL (IGCSE) – PHYSICS
Section 2 Thermal Physics
Specific Latent Heat
The amount of energy per unit mass absorbed or released
during a change of phase
DQ
l=
m
(J /kg)
Molecular Interpretation: At a phase transition bonds are being broken or
formed. This gives an associated intake or release of
energy.
• Describe an experiment to measure specific latent heats for steam and for ice
SPECIFIC LATENT HEAT OF STEAM
A
V
l=
ItV
m1 – m2
Heater
00250.0g




Take a volume of liquid to its boiling point
Measure the mass of the liquid
Boil the water for a fixed period and calculate the energy input by measuring the
voltage and current for the heater
Record the mass of the liquid after heating and calculate the mass turned to a gas
DIPONT Educational Resource – Science
14
PAL (IGCSE) – PHYSICS
Section 2 Thermal Physics

SPECIFIC LATENT HEAT OF ICE
A
V
Ice
Heater
Melted Water
ItV
l=
m1 – m2
00250.0g




Heat the ice until it starts to melt
Capture the melted ice in the beaker on the balance
Heat for a fixed length of time and calculate the energy input by measuring the
voltage and current supplied to the heater
Measure the mass of water melted in that period
2.3 Transfer of thermal energy
2.3 (a) Conduction
Core
• Describe experiments to demonstrate the properties of good and bad conductors of heat
Wax
Heat Source
Good Conductor
Coin
Medium Conductor
Poor Conductor



Coins or other objects can be attached to a object to be tested
One end of the object is then heated
The ability of the object to conduct heat can be judged by how quickly the
wax melts and so coins are released
DIPONT Educational Resource – Science
15
PAL (IGCSE) – PHYSICS
Section 2 Thermal Physics
Supplement
• Give a simple molecular account of heat transfer in solids
Conduction
HOT
COLD
Transfer of Thermal Energy
2.3 (b) Convection
Core
• Relate convection in fluids to density changes and describe experiments to illustrate
convection
Convection
Convection
Currents
Cold air is less dense
and so sinks down
Hot air is less dense
and so is forced up
2.3 (c) Radiation
Core
• Identify infra-red radiation as part of the electromagnetic spectrum
Electromagnetic Spectrum
Wavelength
3 x 104 m
3 x 10-4 m
3m
3 x 10-12 m
3 x 10-8 m
Infrared
Gamma rays
Ultraviolet
Radio waves
X-rays
Microwaves
104 Hz
108 Hz
1012 Hz
1016 Hz
1020 Hz
Frequency
7.5 x 10-7 m
4 x 10-7 m
7.5 x 1014 Hz
4 x 1014 Hz
Visible Light
DIPONT Educational Resource – Science
16
PAL (IGCSE) – PHYSICS
Section 2 Thermal Physics
Supplement
• Describe experiments to show the properties of good and bad emitters and good and bad
absorbers of infra-red radiation
Black surface
Shiny surface
Coin
Heat Source
PROPERTIES OF EMMITERS
Wax
Black surface
Heat Source
Shiny surface
PROPERTIES OF ABSORBERS
2.3 (d) Consequences of energy transfer
Core
• Identify and explain some of the everyday applications and consequences of conduction,
convection and radiation
Energy Transfer
Conduction
Applications
Saucepan or wok
Convection
Air conditioner
Radiation
Paint
DIPONT Educational Resource – Science
Consequences
Made of copper or other
good conductors
Normally placed on the
ceiling as cold air drops
In hot climates houses are
painted white
17