Contents
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2 Thermal energy transfer . . . . . . . . . . . . . . . . . . . . . . 1
3 Gas Laws . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4 Kinetic Theory of gasses . . . . . . . . . . . . . . . . . . . . . . 7
5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1 Introduction
Thermal physics is a combination of three areas of study in physics which include
Statistical Physics(which aims to describe physical phenomena by using statis-
tical methods and probability theory),Thermodynamics(the study of heat, work
and temperature and their relation to energy and entropy) and Kinetic theory
of gases which is a classical model for the thermodynamic behaviour of gasses;
modelling them as submicroscopic particles in constant, random motion. Thank-
fully in this topic we will only worry about the results from these three branches
of physics and mainly ignore the underlying math which can become quite com-
plex.
2 Thermal energy transfer
The internal energy of a substance is equal to the sum of the kinetic and potential energies
of all it’s particles. Since the particles move randomly this means that the poten-
tial and kinetic energies are randomly distributed throughout the substance.
We can increase the internal energy of a system by doing two things;
• We can do work on the system i.e by moving particles or changing the
shape by applying a force.
• Increasing the temperature of the system will increase the kinetic energy
of the constituent particles thus increase the internal energy.
, When the state of a substance changes,its internal energy also changes. This is
due to the fact that the potential energy of the substance changes while the ki-
netic energy remains constant. A good example is that of frozen water; the water
reaches its freezing point of 0∘ c and its kinetic energy remains constant while the
potential energy decrease as Hydrogen bonds within the object form.
Given below is the graph of temperature 𝑇 against internal energy 𝑈 of a sub-
stance:
𝑇
Gas
Liquid
Boiling Point
Solid
Melting Point
𝑈
The amount of heat gained or lost by a substance 𝑄 is given by the equation,
𝑄 = 𝑚𝑐Δ𝜃 (0.1)
where 𝑚 is the mass of substance, 𝑐 is the specific heat capacity of the sub-
stance(which is substance specific) and Δ𝜃 is the change in temperature expe-
rienced by the substance given in Kelvin(K).
The Specific heat capacity of a substance is defined to be - The amount of
energy required to increase the temperature of 1kg of a substance by 1∘ c/1K,
without changing its state.
By using some dimensional analysis we can easily find the units of 𝑐, to start
we know that the units of heat is J thus we have,
[𝑄] = J = [𝑚𝑐Δ𝜃] = Kg K ⋅ 𝑋
2
1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
2 Thermal energy transfer . . . . . . . . . . . . . . . . . . . . . . 1
3 Gas Laws . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4 Kinetic Theory of gasses . . . . . . . . . . . . . . . . . . . . . . 7
5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
1 Introduction
Thermal physics is a combination of three areas of study in physics which include
Statistical Physics(which aims to describe physical phenomena by using statis-
tical methods and probability theory),Thermodynamics(the study of heat, work
and temperature and their relation to energy and entropy) and Kinetic theory
of gases which is a classical model for the thermodynamic behaviour of gasses;
modelling them as submicroscopic particles in constant, random motion. Thank-
fully in this topic we will only worry about the results from these three branches
of physics and mainly ignore the underlying math which can become quite com-
plex.
2 Thermal energy transfer
The internal energy of a substance is equal to the sum of the kinetic and potential energies
of all it’s particles. Since the particles move randomly this means that the poten-
tial and kinetic energies are randomly distributed throughout the substance.
We can increase the internal energy of a system by doing two things;
• We can do work on the system i.e by moving particles or changing the
shape by applying a force.
• Increasing the temperature of the system will increase the kinetic energy
of the constituent particles thus increase the internal energy.
, When the state of a substance changes,its internal energy also changes. This is
due to the fact that the potential energy of the substance changes while the ki-
netic energy remains constant. A good example is that of frozen water; the water
reaches its freezing point of 0∘ c and its kinetic energy remains constant while the
potential energy decrease as Hydrogen bonds within the object form.
Given below is the graph of temperature 𝑇 against internal energy 𝑈 of a sub-
stance:
𝑇
Gas
Liquid
Boiling Point
Solid
Melting Point
𝑈
The amount of heat gained or lost by a substance 𝑄 is given by the equation,
𝑄 = 𝑚𝑐Δ𝜃 (0.1)
where 𝑚 is the mass of substance, 𝑐 is the specific heat capacity of the sub-
stance(which is substance specific) and Δ𝜃 is the change in temperature expe-
rienced by the substance given in Kelvin(K).
The Specific heat capacity of a substance is defined to be - The amount of
energy required to increase the temperature of 1kg of a substance by 1∘ c/1K,
without changing its state.
By using some dimensional analysis we can easily find the units of 𝑐, to start
we know that the units of heat is J thus we have,
[𝑄] = J = [𝑚𝑐Δ𝜃] = Kg K ⋅ 𝑋
2
