VI Thermal Physics

Ice Point: Melting point of pure ice at atmospheric pressure (0°C)
Steam Point: Boiling point of water at atmoshperic pressure (100°C)
Absolute Zero: -273°C (obtained by considering that gas pressure varied with temperature)

Kelvins (KK): Absolute scale of temperatures

xK=x°C+273xK = x°C + 273

Heat Transfer

Heat is transferred from one object to another by touch. Thermal equilibrium describes objects that have no heart transfer occuring between them because they are at the same temperature.


Takes place in solids, liquids and gases. Occurs like electrical conduction cia free electrons in the substances. Insulating materials have very small amounts of free electrons and thus inhibit heat transfer via conduction.


Process of circulation in liquids and gases due to density differences.


Is emitted from every surface. The more heat is present in the surface of a substance the more energy it emits via radiation that can travel through a vacuum.

Thermal Properties of Materials

Strong bonds within molecules are responsible for rigid solid substances. The molecules of liquid substances possess comparatively weak bonds. Molecules in gases move about freely. Thermal energy is stored in the particles of substances. The amount of heat energy can affect the aforementioned bonds.


A solid becoming a liquid


A liquid becoming a solid


A gas becoming a liquid


A liquid becoming a gas

Specific Heat Capacity

The energy required to increase the temperature of 1kg of mass (unit mass) by one degree °C.

Formula to raise the temperature from T1T1 to T2T2:

ΔE=mc(T2T1)\Delta E = mc(T2 - T1)

c=Specific Heat Capacity(J/kg/°C)c = \text {Specific Heat Capacity} (J/kg/°C)

c=ΔEm(T2T1)c = \frac{\Delta E}{m(T2-T1)}

Substance Specific Heat Capacity
Water 4200J
Copper 380J
Aluminium 900J
Ice 2100J

Specific Latent Heat

The energy required by a material of unit mass to change its state. That is, the point beyond which heat energy is used to break bonds and no longer stored.

ΔE=ml\Delta E = ml

l=Specific Latent Heat (J/kg)l = \text{Specific Latent Heat (J/kg)}

Substance Specific Latent Heat
Ice 336kJ/kg
Steam 2.3MJ/kg

First Law of Thermodynamics

An engine accepts heat from a high temperature source (Q1Q1) and loses some heat to a low temperature sink (Q2Q2).

W=Q1Q2W = Q1 - Q2

States that energy in an isolated system is conserved.

Second Law of Thermodynamics

Energy tends to spread out and become less useful whenever it is transferred between objects of a system.

Heat Engine

The low temperature sink is required to prevent moving parts from overheating.

Maxmimum Efficiency=T1T2T1\text{Maxmimum Efficiency} = \frac {T1 - T2}{T_1}

The lower the temperature of the sink, the more efficient the engine.