Simplified notes for SPM Students

1. Thermal Energy
Form 4 Physics (SPM) – Chapter 4

2. Thermodynamics

1st Law: Energy is conserved. i.e. It can’t be created or
destroyed, only transferred from one form to another

3. Definitions

Thermal Energy


Temperature


Total mechanical energy contained in a body
Degree of hotness or coldness of a body
Heat

The transfer of energy from one system to another

4. 


Thermal energy depends on the temperature, number of
particles and arrangement of particles in a body
Heat on the other hand is thermal energy moving from
one place to another
Temperature depends on kinetic energy in an object

5. Heat and Temperature

Similarities



Both are quantitative (measureable)
Both are scalar quantities (no direction)
Differences


Temperature is measured in Kelvin (SI unit) with a
thermometer
Heat is measured in Joule (Derived unit) with a joulemeter or
calorimeter

6. Thermal Equilibrium


State where there is no net heat transfer between two or
more systems, resulting in constant temperature
0th Law of Thermodynamics

8. 

Heat exchange between System A and System B occurs
through thermal conduction
Time taken for both systems to reach thermal
equilibrium depends on the rate of heat transfer

9. Thermometer

A good thermometer has




Suitable thermometric liquid
Thin bulb to allow quicker response to heat
Thin capillary tube to increase sensitivity
Thick glass bore to allow magnification of scale for easier
reading and for increased durability
Capillary tube
Glass bore with scale

10. 
Thermometric properties


Properties that change with changing temperature
Example



When temperature , object expands (volume )
When temperature , pressure
When temperature , electrical resistance

11. Thermometric fluid

Properties:





Should be easily seen
Able to expand and contract uniformly with temperature
Does not stick to wall of capillary tube
Good heat conductor
Types:

Mercury


Opaque and suitable for measuring high temperatures due to high
boiling point and non-volatility
Alcohol

Volatile and very low melting point makes it suitable for measuring
low temperatures

12. Thermometer - Calibration

Thermometer placed in melting ice has a column length
of l0

When placed in boiling water, the length is

Thermometer placed in a solution of unknown
temperature has a length of lϴ
l100

13. Based on the recordings, 100˚C = (l100 – l0)
and Unknown temperature, ϴ = (lϴ – l0)
Proportionally,
=
ϴ
100 ˚C
Hence,
ϴ
=
(lϴ – l0)
(l100 – l0)
(lϴ – l0)
(l100 – l0)
X
100 ˚C

14. Heat Capacity



The amount of heat change required to change the
temperature of an object by 1˚C
Heat capacity, C = ∆Q/ ∆T , where ∆Q = Heat change
and ∆T = Temperature change
Unit = J˚C-1

15. Specific Heat Capacity

Amount of heat change required to change the
temperature of a 1kg object by 1˚C
Specific means a unit quantity of a physical property (in
this case, mass)
Specific heat capacity, c = ∆Q/(m∆T) , where m = mass.

Unit = Jkg-1˚C-1



16. Observations of SHC

Sea breeze



During the day, temperature of air above land rises quicker
than air above sea (land has a lower SHC than the sea)
This warmer air moves upwards and toward the sea, creating a
convection current
The cooler sea acts as a heat sink for this warm air, causing air
above the sea level to blow inland to replace risen air

17. 
Land breeze



During the night, the sea is warmer than the land due to
accumulated heat gained during the day becomes enough to
raise its temperature.
Air above the sea is now warmer causing the air above the sea
to rise upwards, flow toward and sink at the land.
The convection current created causes the air above the land
to blow towards the sea

18. Sea Breeze
Ocean is cooler than land (cold source, a.k.a. heat sink)

19. Land Breeze
Ocean is warmer than land (heat source)

20. This means…

A body with high SHC will heat or cool slower
(i.e. poor conductor)

A body with low SHC will heat or cool faster (i.e.
good conductor)

Water has a very high SHC value (4200 Jkg-1˚C-1). It’s
suitable as a ‘coolant’ in engines and machines to sink
heat away from hot components
Water is used as coolant in cooling systems, radiators
and the mammalian body


21. Change in physical state

22. Heating

At gradients:


Heat absorbed  Kinetic energy (Temperature rises)
At plateaus:


Heat absorbed is used to overcome bonds
Kinetic energy (and temperature) is constant (melting and
boiling point)

23. Cooling

At gradients:


Kinetic energy  Heat released (Temperature drops)
At plateaus:


Rebonding releases heat energy
Kinetic energy (and temperature) is constant (condensation
and freezing point)

25. Techniques

Insulation


Prevents heat loss or gain from the surroundings
Stirring with the thermometer


To ensure even heating and cooling.
If stirring is uneven during cooling, supercooling (liquid state
below freezing point) occurs

26. 
At gradients of both curves


The heat change is causing a change in temperature. This heat
is the heat capacity
At the plateaus of both curves:

The heat change occurs at constant temperature. This is
latent heat

27. Latent Heat



Heat change that occurs when a substance changes its
physical state at constant temperature
Latent heat, L = ∆H, where ∆H = Heat change
Unit = Joule (J)

28. Specific Latent Heat



Heat change that occurs when 1kg of substance changes
its physical state at constant temperature
Specific latent heat, L = ∆H/m , where ∆H = Heat
change and m = mass
Unit = Jkg-1

29. Two types of specific latent heat

Specific latent heat of fusion (Lf)


Heat change that occurs when 1kg of substance changes between
the solid and liquid phases with no change in temperature
Specific latent heat of vapourisation (Lv)

Heat change that occurs when 1kg of substance changes between
the liquid and gas phases with no change in temperature

30. Applications of Latent Heat

Steam cooking


Steam has a high latent heat and when it condenses on food,
the heat released is used to cook the food.
Sweating

Evaporation of sweat makes us feel cold because when water
evaporates, the latent heat of vapourisation is absorbed from
the surface of the skin, thus cooling it down.

31. Ideal Gas





An idealistic paradigm of gases in real life
The absolute zero is the temperature where all motion
of ideal gas particles ceases (Kinetic energy = 0)
The absolute zero is -273 ˚C
The absolute zero scale is Kelvin (K)
0K = -273 ˚C

32. Ideal Gas Laws

Boyle’s Law



Charles’ Law



Pressure of a gas is inversely proportional to its volume at
constant temperature
P1V1 = P2V2
Volume of a gas is directly proportional to its temperature in
the absolute zero scale at constant pressure
V1/T1 = V2/T2
Pressure Law


Pressure of a gas is directly proportional to its temperature in
the absolute zero scale at constant volume
P1/T1 = P2/T2

33. Boyle’s Law
Charles’ Law
Pressure Law

34. Universal Gas Law
P1V1 / T1 = P2V2 / T2