If Δ U and Δ W represent the increase in internal energy and work done by the system respectively in a thermodynamical process, which of the following is true? (a) Δ U = -Δ W, in an adiabtic process (b) Δ U = Δ W, in an isothermal process (c) Δ U = Δ W, in an adiabatic process (d) Δ U = - Δ W, in an isothermal process

Answer: (a). First law: Q = Δ U + Δ W. Adiabatic: Q = 0 ⇒ Δ U = -Δ W. Isothermal (ideal gas): Δ U = 0, so (b) and (d) fail. So the answer is (a).

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Thermodynamic Processes

If $\Delta$ U and $\Delta$ W represent the increase in internal energy and work done by the system respectively in a thermodynamical process, which of the following is true?

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Answer: (a)

First law: $Q = \Delta U + \Delta W$ .
Adiabatic: $Q = 0 \Rightarrow \Delta U = -\Delta W$ .
Isothermal (ideal gas): $\Delta U = 0$ , so (b) and (d) fail.
So the answer is (a).

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