Gujarati
Hindi
11.Thermodynamics
hard

One mole of 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

A

The change in internal energy in the process $AB$ is $-350\,R$

B

The change in internal energy in the process $BC$ is $-500\,R$

C

The change in internal energy in whole cyclic process is $250\,R$

D

The change in internal energy in the process $CA$ is $700\,R$

Solution

For a diatomic gas,

$C_{v}=\frac{5}{2} R$

$\Delta U_{B A}=n C_{V}\left(T_{B}-T_{A}\right)=1 \times \frac{5 R}{2}(800-400)=1000 R$

$\Delta U_{A C}=\Delta Q_{A C}-W_{A C}=n C_{P}\left(T_{A}-T_{C}\right)-n R\left(T_{A}-T_{C}\right)=n C_{V}\left(T_{A}-T_{C}\right)=1 \times$

$\frac{5 R}{2}(400-600)=-500 R$

Thus, adding up the change in internal energy in both these processes, we get change in internal energy from $\mathrm{C}$ to $\mathrm{B}$ as $500 \mathrm{R}$.

As the change in internal energy is a point function we get $U_{B C}=-500 R$

Standard 11
Physics

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