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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

A gas has an internal energy given by the relation U = 1.5 pV . The...

A gas has an internal energy given by the relation U=1.5pVU = 1.5 pV. The gas expands from 100 cm3100 \text{ cm}^3 to 200 cm3200 \text{ cm}^3 against a constant pressure of 1.0×105 Pa1.0 \times 10^5 \text{ Pa}. Determine the heat absorbed by the gas during this process.

Options

  1. A35 J35 \text{ J}
  2. B25 J25 \text{ J}
  3. C15 J15 \text{ J}
  4. D10 J10 \text{ J}

Correct answer

B. 25 J25 \text{ J}

Step-by-step solution

The process is isobaric, so the pressure pp of the gas is constant and equal to the external pressure.

The work done by the gas during the expansion is given by W=pΔV=p(V2−V1)W = p \Delta V = p(V_2 - V_1).

Substituting the given values:

W=1.0×105×(200−100)×10−6=1.0×105×10−4=10 JW = 1.0 \times 10^5 \times (200 - 100) \times 10^{-6} = 1.0 \times 10^5 \times 10^{-4} = 10 \text{ J}

The change in internal energy is ΔU=U2−U1=1.5p2V2−1.5p1V1\Delta U = U_2 - U_1 = 1.5 p_2 V_2 - 1.5 p_1 V_1.

Since the pressure is constant, p1=p2=pp_1 = p_2 = p, giving ΔU=1.5p(V2−V1)=1.5W\Delta U = 1.5 p(V_2 - V_1) = 1.5 W.

ΔU=1.5×10=15 J\Delta U = 1.5 \times 10 = 15 \text{ J}

According to the first law of thermodynamics, the heat absorbed by the gas is ΔQ=ΔU+W\Delta Q = \Delta U + W.

ΔQ=15+10=25 J\Delta Q = 15 + 10 = 25 \text{ J}
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