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One mole of a diatomic ideal gas undergoes a cyclic process $ABC$ as shown in figure. The process $BC$ is adiabatic. The temperatures at $A, B$ and $C$ are $400\ K, 800\ K $ and $600\ K$ respectively. Choose the correct statement

The change in internal energy in the process $CA$ is $700\ R$
The change in internal energy in the process $AB$ is $ -350R$
The change in internal energy in the process $BC$ is $-500R$
The change in internal energy in whole cyclic process is $250R $
Solution
In cyclic process, change in total internal energy is zero.
$\Delta {U_{cyclic}} = 0$
$\Delta {U_{BC}} = n{C_v}\Delta T = 1 \times \frac{{5R}}{2}\Delta T$
$Where,{C_v} = molar\,specific\,heat\,at\,constant\,volume.$
$For\,BC,\Delta T = – 200K$
$\therefore \,\,\Delta {U_{BC}} = – 500R$