Question

When the temperature of a body is equal to that of the surroundings then the body appears
A. In the thermal equilibrium
B. red
C. cold
D. hot

Answer 1

Hint: Generally when temperature difference is maintained then heat transfers from higher temperature body to the lower temperature body. The amount of heat transferred depends upon the various factors like the temperature difference, thermal resistance of the material.

Complete answer:
Flow of any quantity with time is known as a current. It can be fluid current or heat current or electric current.
In case of fluid current a pressure difference is maintained and that drives the flow of fluid and fluid always flows from high pressure region to the low pressure region and fluid current is governed by fluid resistance too.
Whereas in electric current the electric charge flows with time and the voltage difference and electric resistance combined will govern the electric current. Charge flows from higher voltage to lower voltage naturally.
Similarly in thermal current it is governed by temperature difference and thermal resistance.
That means thermal current keeps on flowing until there is a temperature difference. When the temperature difference becomes zero then heat will not flow. That means the temperature of the body and the heat source will become equal. Here the heat source is surroundings, so when temperatures become equal we call the body is in thermal equilibrium with surroundings.

So, the correct answer is “Option A”.

Note:
The word equilibrium is used when some quantity is in a balanced state. In mechanics we use terms translational equilibrium rotational equilibrium when there is no net force and no net torque respectively. Here we use thermal equilibrium when there is no net temperature difference between the body and the surroundings.