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HPCET Thermodynamics — practice questions — page 2

Explore 36 free Thermodynamics questions in HPCET Physics. Open each question or exercise to read its content, reference answers and available explanation.

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Thermodynamics questions and exercises with answers

Showing questions 31–36 of 36.

A heat engine operates with 20% efficiency between two reservoirs. If T_h = 500 K, find T_c (for maximum/Carnot):Read the answer and worked solution →An ideal gas undergoes isothermal expansion at 300 K from V = 1 to V = 2. Heat absorbed (n = 1):Read the answer and worked solution →A diatomic ideal gas at 27°C is compressed adiabatically to ½ its volume. Find final temperature (γ = 7/5):Read the answer and worked solution →NEET · Physics · Thermodynamic ProcessesRead the answer and worked solution →n-type or p-type?Read the answer and worked solution →True or false: semiconductorsRead the answer and worked solution →

Worked practice questions

A heat engine operates with 20% efficiency between two reservoirs. If T_h = 500 K, find T_c (for maximum/Carnot):

  1. 450 K
  2. 300 K
  3. 400 K
  4. 100 K
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Correct answer: C. 400 K

We have η = 1 - T_c/T_h → 0.20. That is η = 1 - T_c/500 → T_c/500. That is η = 0.80 → T_c. So η = 400 K.

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An ideal gas undergoes isothermal expansion at 300 K from V = 1 to V = 2. Heat absorbed (n = 1):

  1. R × 300 × ln(1/2)
  2. R × 300
  3. R × 300 × ln 2
  4. R × 600
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Correct answer: C. R × 300 × ln 2

In isothermal expansion at T, Q = W = nRT ln(Vf/Vi) = 1 × R × 300 × ln(2/1) = 300R ln 2 ≈ 208R J.

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A diatomic ideal gas at 27°C is compressed adiabatically to ½ its volume. Find final temperature (γ = 7/5):

  1. 600 K
  2. 395 K
  3. 240 K
  4. 420 K
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Correct answer: B. 395 K

T₁V₁^(γ-1) = T₂V₂^(γ-1). T₁ = 300 K, V₂ = V₁/2. T₂ = T₁(V₁/V₂)^(γ-1) = 300 × 2^0.4 ≈ 300 × 1.32 ≈ 396 K. Adiabatic compression heats the gas.

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