Carnot engine: You want to design an ideal Carnot heat engine that wastes only 35.0% of the heat that goes into it. The lowest cold-reservoir temperature available to you is +15.0°C. If 150.0 J of work is done per cycle, the heat input per cycle is closest to
A) 203 J.
B) 231 J.
C) 248 J.
D) 429 J.
E) 760 J.

Question

Quizplus · Accepted Answer

The efficiency of a Carnot engine is given by η = 1 - (Tc/Th), where Tc and Th are the absolute temperatures of the cold and hot reservoirs, respectively. If 35% of the heat is wasted, the efficiency is 65% or 0.65. The work done per cycle is 150 J, so the heat input Qh is W/η = 150 J / 0.65 ≈ 231 J.

Carnot Engine: You Want to Design an Ideal Carnot Heat