Задача 20764.

The temperature of the heater of a thermal machine operating in the Carnot cycle, 480 K, the temperature of the refrigerator 390 K. What should be the temperature of the heater with the temperature of the refrigerator unchanged, so that the efficiency of the machine is doubled?

A detailed solution with a brief entry of the condition, formulas and laws used in the solution, the derivation of the calculation formula and the answer.
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