Question

1)Explain why two bodies at different temperatures if brought together in thermal contact do not necessarily attain their mean temperatures?

2)A piece of lead is hammered.Does the internal energy change?Does heat enter the lead from outside?

3)Why do birds swell their feathers during winter?

Answer 1

1)

When two bodies at different temperatures T1 and T2 are brought in thermal contact, heat flows from the body at the higher temperature to the body at the lower temperature till equilibrium is achieved, i.e., the temperatures of both the bodies become equal. The equilibrium temperature is equal to the mean temperature (T1 + T2)/2 only when the thermal capacities of both the bodies are equal.

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2)

The kinetic energy of the hammer would be converted into thermal energy upon impact which would be transferred into the material. Thi thermal energy would increase the internal energy of the system as the molecules absorb the resulting heat.

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3)

Birds swell up their feathers in order to provide more insulation to their bodies by trapping more air in between them, this protects them for the severity of the cold outside. Air, as we know is the best form of insulating material nature has provided.