Question:medium

A heat engine operates between a cold reservoir at temperature 300 K and a hot reservoir at temperature \(T_1\). It takes 200 J of heat from the hot reservoir and delivers 120 J of heat to the cold reservoir in a cycle. The minimum temperature \(T_1\) of the hot reservoir is:

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For heat engine problems, use efficiency \(\eta = \frac{W}{Q_H}\) and compare with Carnot efficiency for limits.
Updated On: Jun 19, 2026
  • 450 K
  • 400 K
  • 500 K
  • 350 K
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The Correct Option is C

Solution and Explanation

Step 1: Engine work output.
W = Q_H - Q_C = 200 - 120 = 80 J.

Step 2: Thermal efficiency.

η = W/Q_H = 80/200 = 0.4.

Step 3: Carnot efficiency bound.

For maximum efficiency (minimum T₁), η = 1 - T_C/T_H → 0.4 = 1 - 300/T₁.

Step 4: Solving for T₁.

300/T₁ = 0.6 → T₁ = 500 K.

Step 5: Conclusion.

The minimum hot reservoir temperature is 500 K.
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