Thermodynamics - Result Question 24

25. 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? [2010, 1998]

(a) $\Delta U=-\Delta W$, in an adiabatic process

(b) $\Delta U=\Delta W$, in an isothermal process

(c) $\Delta U=\Delta W$, in an adiabatic process

(d) $\Delta U=-\Delta W$, in an isothermal process

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Answer:

Correct Answer: 25. (a)

Solution:

  1. (a) By first law of thermodynamics, $\Delta Q=\Delta U+\Delta W$ In adiabatic process, $\Delta Q=0$

$\therefore \Delta U=-\Delta W$

In isothermal process, $\Delta U=0$

$\therefore \Delta Q=\Delta W$