Thermodynamics - Result Question 34

36. A thermodynamic process is shown in the figure. The pressures and volumes corresponding to some points in the figure are

$P_A=3 \times 10^{4} Pa$

$V_A=2 \times 10^{-3} m^{3}$

$P_B=8 \times 10^{4} Pa$

$V_D=5 \times 10^{-3} m^{3}$.

In process $A B, 600 J$ of heat is added to the system and in process $BC, 200 J$ of heat is added to the system. The change in internal energy of the system in process $A C$ would be

(a) $560 J$

(b) $800 J$

(c) $600 J$

(d) $640 J$

[1991]

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Answer:

Correct Answer: 36. (a)

Solution:

  1. (a) $B C$ is isobaric process,

$ \begin{aligned} & \therefore \quad W=P_B \times(V_D-V_A)=240 J \\ & \Delta Q=600+200=800 J \\ & \text{ Using } \Delta Q=\Delta U+\Delta W \\ & \Rightarrow \Delta U=\Delta Q-\Delta W=800-240=560 J \end{aligned} $

Since $A B$ is an isochoric process i.e., $\Delta V=0$ so, no work is done.