Thermal Physics:
Q. Describe a system in thermal equilibrium.
In a system in thermal equilibrium, no heat transfer occurs within the system or between the system and those adjacent. The implication is therefore that the system is isolated and has a constant internal temperature.
Q. Why is the absolute scale (Kelvin scale) used?
It doesn't arbitrarily depend on the properties of a given substance.
Q. What is meant by the specific heat capacity of a substance?
The amount of heat energy required to raise the temperature of 1 kg of the substance by 1 degree Celsius. Heat capacity has the unit J/kgK.
Q. Define the specific latent heat of a substance.
The specific latent heat of a substance is the heat energy required to change the state of 1kg of a substance, without changing its temperature.
Q. What is the difference between the specific latent heat of fusion and the specific latent heat of vaporisation?
The latent heat of fusion refers to the transition from a solid to a liquid state, where the latent heat of vaporisation refers to the transition from a liquid to a gaseous state.
Q. Why is the specific latent heat of vaporisation higher than the specific latent heat of fusion for the same substance?
The energy required to completely separate the molecules is greater than that required to go from solid to liquid. From solid to liquid, forces of attraction still exist between the molecules, whereas from liquid to gas, they are almost 0.
Q. Describe the distinction between work being done by a gas and work being done on a gas?
Work is done on a gas when it is compressed, i.e. the temperature of a constant volume of gas is increased or if the volume itself is decreased. Work is done by the gas if it expands due to a temperature increase (while sustaining a constant pressure).
Q. What is the first law of thermodynamics?
Change in U = Q + W
Where U is Internal energy, Q is the heat added to a system and W is the work done by the system.
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