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Concepts Of Physics MCQ Edition [Volume 2]
Exam
Concepts Of Physics MCQ Edition [Volume 2]
Subject
Physics
Chapter
Laws of Thermodynamics

Concepts Of Physics MCQ Edition [Volume 2] · Physics · Laws of Thermodynamics

Two processes on a system are illustrated in the figure. The...

Two processes on a system are illustrated in the figure. The volumes of the initial states are identical for both processes, and the volumes of the final states are also identical. Let ΔW1\Delta W_1 and ΔW2\Delta W_2 denote the work done by the system in processes AA and BB, respectively.
Two processes on a system are illustrated in the figure. The volumes of the initial states are identical for both

Options

  1. AΔW1=ΔW2\Delta W_1 = \Delta W_2
  2. BΔW1>ΔW2\Delta W_1 > \Delta W_2
  3. CThe relation between ΔW1\Delta W_1 and ΔW2\Delta W_2 cannot be established.
  4. DΔW1<ΔW2\Delta W_1 < \Delta W_2

Correct answer

D. ΔW1<ΔW2\Delta W_1 < \Delta W_2

Step-by-step solution

From the given p−Tp-T graph, both processes A and B are represented by horizontal lines, which means they are isobaric (constant pressure) processes.

Let the pressure of process A be pAp_A and that of process B be pBp_B. From the graph, it is clear that pB>pAp_B > p_A.

The work done by the system in an isobaric process is given by ΔW=pΔV=p(Vf−Vi)\Delta W = p \Delta V = p(V_f - V_i).

It is given that the initial volumes for both processes are identical (Vi,A=Vi,B=ViV_{i,A} = V_{i,B} = V_i) and the final volumes are also identical (Vf,A=Vf,B=VfV_{f,A} = V_{f,B} = V_f). Therefore, the change in volume ΔV=Vf−Vi\Delta V = V_f - V_i is the same for both processes.

From the graph, the temperature TT increases in both processes. For an ideal gas at constant pressure, V∝TV \propto T, so the volume must increase, implying ΔV>0\Delta V > 0.

The work done in process A is ΔW1=pAΔV\Delta W_1 = p_A \Delta V.

The work done in process B is ΔW2=pBΔV\Delta W_2 = p_B \Delta V.

Since pB>pAp_B > p_A and ΔV>0\Delta V > 0, we have pBΔV>pAΔVp_B \Delta V > p_A \Delta V.

Therefore, ΔW2>ΔW1\Delta W_2 > \Delta W_1, which can be written as ΔW1<ΔW2\Delta W_1 < \Delta W_2.
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