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Concepts Of Physics MCQ Edition [Volume 2]
Exam
Concepts Of Physics MCQ Edition [Volume 2]
Subject
Physics
Chapter
Specific Heat Capacities of Gases

Concepts Of Physics MCQ Edition [Volume 2] · Physics · Specific Heat Capacities of Gases

Three samples A , B and C of the same gas ( γ = 1.5 ) initially...

Three samples AA, BB and CC of the same gas (γ=1.5\gamma = 1.5) initially have equal volumes and temperatures. Each sample's volume is doubled, with the process being isothermal for AA, adiabatic for BB, and isobaric for CC. If the final pressures are equal for all three samples, determine the ratio of their initial pressures.

Options

  1. A1:2:221 : 2 : 2\sqrt{2}
  2. B2:22:12 : 2\sqrt{2} : 1
  3. C22:2:12\sqrt{2} : 2 : 1
  4. D2:3:12 : 3 : 1

Correct answer

B. 2:22:12 : 2\sqrt{2} : 1

Step-by-step solution

Let the initial volume of each sample be V0V_0 and the final pressure of each sample be PfP_f.

For sample AA (isothermal process):
PAV0=Pf(2V0)⇒PA=2PfP_A V_0 = P_f (2V_0) \Rightarrow P_A = 2P_f

For sample BB (adiabatic process):
PBV0γ=Pf(2V0)γP_B V_0^{\gamma} = P_f (2V_0)^{\gamma}
Given γ=1.5=32\gamma = 1.5 = \dfrac{3}{2},
PB=Pf(2)3/2=22PfP_B = P_f (2)^{3/2} = 2\sqrt{2}P_f

For sample CC (isobaric process):
Pressure remains constant, so PC=PfP_C = P_f

The ratio of their initial pressures is:
PA:PB:PC=2Pf:22Pf:Pf=2:22:1P_A : P_B : P_C = 2P_f : 2\sqrt{2}P_f : P_f = 2 : 2\sqrt{2} : 1
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