A heat engine has a hot reservoir of 680°C and a cold reservoir of 220°C. What is the efficiency of the engine?

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680C = 273+680 = 953 K

220 C = 273 + 220 = 493 K

e = (953-493)/953 = .483

IF and ONLY IF it is a Carnot cycle heat engine (maximum efficiency)

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To find the efficiency of a heat engine, you can use the formula:

Efficiency = 1 - (Tc/Th)

Where Tc is the temperature of the cold reservoir and Th is the temperature of the hot reservoir.

In this case, Tc = 220°C and Th = 680°C.

Substituting these values into the formula we get:

Efficiency = 1 - (220/680)

Simplifying this equation:

Efficiency = 1 - 0.3235294117647059

Efficiency ≈ 0.6765 (rounded to four decimal places)

Therefore, the efficiency of the heat engine is approximately 0.6765 or 67.65%.