An iron bar at 200°C is placed in thermal contact with an identical iron bar at 120°C in an isolated system. After 30 minutes, both iron bars are at 160°C. If the iron bars were placed in thermal contact in an open system instead of an isolated system, how would the results be different? Assume that the room temperature is 25°C.

A.

The temperatures of the iron bars after 30 minutes would be less than 160°C because heat would be lost to the surroundings.

B.

It would take more than 30 minutes for both iron bars to reach 160°C because heat would be transferred less efficiently.

C.

The temperatures of both iron bars would increase as they absorb heat from the surroundings.

D.

The temperatures of both iron bars would decrease because pieces of them would be lost to the surroundings.

Answer: The correct answers are A and B.

Explanation:

Conduction: In the conduction, the heat is transferred from the hotter body to the colder body until the temperature on both bodies are equal.

In thermal equilibrium, there is no heat transfer as the heat is transferred till the temperature on the bodies are not same.

In the given problem, an iron bar at 200°C is placed in thermal contact with an identical iron bar at 120°C in an isolated system. After 30 minutes, the thermal equilibrium is attained. Then, the temperature on both iron bars are equal. Both iron bars are at 160°C in an isolated system.

But in an open system, the temperatures of the iron bars after 30 minutes would be less than 160°C. There will be heat lost to the surrounding. The room temperature is 25°C. There will be exchange of the heat occur between the iron bars and the surrounding. But It would take more than 30 minutes for both iron bars to reach 160°C because heat would be transferred less efficiently.

Therefore, the correct options are (A) and (B).

1. A

2. B

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