1. What is zeroth law of thermodynamics?

Ans:

If body A and body B are in thermal equilibrium with body C separately then body A and body B Will be in thermal equilibrium with each other.
NOTE: examiner may ask what’s thermal equilibrium ( its equality of temperature, no temperature gradient. Temperature is same all over the system)

2.What is thermal conductivity?

Ans:

When a system gains heat, it stores some of its heat energy and transports the remaining heat energy to some other system. The ability of a system to transport heat energy is referred to as Thermal conductivity of the system. Basically, it is a Transport property of a system

3.What is the statement of Fourier’s law?

Ans:

The Fourier’s law is the governing law for heat conduction. It states that the rate of heat conduction through a plane layer is proportional to the temperature gradient across the layer and the heat transfer area of the layer.
(Basically, it is an empirical relation between the rate of heat conduction heat transfer and temperature gradient in the direction of heat flow.)

4. Define enthalpy, entropy.

Ans:

Enthalpy: Enthalpy is the measurement of energy in a thermodynamic system. The quantity of enthalpy equals to the total content of heat of a system, equivalent to the system’s internal energy plus the product of volume and pressure.
Entropy: the measure of a system's thermal energy per unit temperature that is unavailable for doing useful work

5.What Is critical radius of insulation?

Ans:

Thickness upto which heat flow increases and after which heat flow decreases is termed as critical thickness. In the case of cylinders and spheres it is called critical radius.

6. What do you mean by thermal contact resistance?

Ans:

Thermal contact resistance is defined as the ratio between this temperature drop and the average heat flow across the interface. According to Fourier's law, the heat flow between the bodies is found by the relation