Question

When two ends of a rod wrapped with cotton are maintained at different temperatures and after some time every point of the rod attains a constant temperature, then
A. Conduction of heat at different points of the rod stops because the temperature is not increasing
B. Rod is a bad conductor of heat
C. Heat is being radiated from each point of the rod
D. Each point of the rod is giving heat to its neighbour at the same rate at which it is receiving heat.

Answer 1

Hint: In order to solve this problem we need to understand thermal equilibrium. When the two physical bodies are said to be in thermal equilibrium if there is no net transfer of heat if they are connected by the path which allows heat transfer.

Complete step by step solution:
When two ends of a rod wrapped with cotton are maintained at different temperatures and after some time every point of the rod attains a constant temperature, then the conduction of heat at different points of the rod will not stop because as the temperature increases, the conduction from atom to atom in a substance also increases. So option 1 is wrong.

If we consider option 2. Whether the rod is a bad or good conductor of heat does not matter once it reaches the constant temperature.

When a body is heated only from the surface the heat is radiated and not from each point or inside a rod. So, option 3 is also wrong.

The rate at which the heat is released at the same rate the heat is receiving from the neighbouring point. Therefore, each point of the rod is giving heat to its neighbour at the same rate at which it is receiving heat.

Hence, option D is the correct answer.

Note: This thermal equilibrium follows the Zeroth Law of Thermodynamics. If the body is said to be in thermal equilibrium, then the two bodies should have the same temperature, if not it will attain the same temperature by releasing or absorbing heat from one body to another thereby attaining the same temperature.