Question:medium

Carnot engine operating between temperatures \(T_1\) and \(T_2\) has efficiency \(0.2\). When \(T_2\) is lowered by \(45\) K, its efficiency becomes \(0.5\). Temperatures \(T_1\) and \(T_2\) are respectively

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Write efficiency = 1 - T2/T1 for both cases and solve.
Updated On: Oct 1, 2026
  • \(150\) K, \(120\) K
  • \(120\) K, \(150\) K
  • \(60\) K, \(80\) K
  • \(80\) K, \(60\) K
Show Solution

The Correct Option is A

Solution and Explanation

Step 1: Use the change in efficiency:
The efficiency rises by $0.3$ when $T_2$ falls by 45 K: $\Delta\eta=\dfrac{\Delta T_2}{T_1}$, so $\dfrac{45}{T_1}=0.3$ and $T_1=150$ K.

Step 2: Find T2:
$\eta=0.2$ gives $T_2=T_1(1-0.2)=120$ K.

Step 3: Pick:
$T_1=150$ K, $T_2=120$ K. Option A.

Final Answer:
Lowering T2 by 45 K raises efficiency by 0.3, so T1 = 150 K and T2 = 120 K. \[ \boxed{\text{(A) }150\ \text{K},\ 120\ \text{K}} \]
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