Q. A gas takes part in two thermal processes in which it is heated from the same initial state to the same final temperature. The two processes are represented on a p – V diagram by straight lines 1 →2 and 1 → 3:

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Figure-1

In which process is the amount of heat supplied to the gas larger?

The amount of heat exchange, by the first law of thermodynamics, is given by

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Figure-2

Since the final temperature of the gas is the same in both the processes, Δ U must be the same in both cases. We then simply have to compare the work done in the two cases:

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Figure-3

Therefore, heat supplied to the gas is more in the process 1 → 3.

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