Home Physics Thermodynamics Heat Engines & Carnot Cycle A Carnot engine take 5000 kcal of heat from …
Physics Thermodynamics Heat Engines & Carnot Cycle Single Correct MCQ
Published on: September 12, 2026

A Carnot engine take 5000 kcal of heat from a reservoir at 727°C and gives heat to a sink at 127°C. The work done by the engine is:

A

3x106 J

B

Zero

C

12.6x106 J

D

8.4x106 J

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Text Solution

Verified by Experts
The correct answer is:
C
  • Temperature Conversion to Kelvin

    Source Temperature:

    T₁ = 727°C + 273 = 1000 K

    Sink Temperature:

    T₂ = 127°C + 273 = 400 K

  • Carnot Efficiency (η)

    η = 1 - (T₂ / T₁) = 1 - (400 / 1000) = 1 - 0.4 = 0.6 (60%)

  • Heat Input Conversion (Q₁)

    Given: Q₁ = 5000 kcal

    Conversion factor: 1 kcal = 4184 J (or 4.184 × 10³ J)

    Q₁ = 5000 × 4184 = 20,920,000 J = 20.92 × 10⁶ J

    (Note: If using the approximation 1 cal ≈ 4.2 J, Q₁ = 5000 × 4200 = 21 × 10⁶ J)

  • Work Done (W)

    W = η × Q₁

    Using 4184 J/kcal:

    W = 0.6 × (20.92 × 10⁶ J) = 12.552 × 10⁶ J ≈ 12.6 × 10⁶ J

    Using 4.2 J/cal (4200 J/kcal):

    W = 0.6 × (21 × 10⁶ J) = 12.6 × 10⁶ J

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