Determine the efficiency of an ideal heat engine if the heater temperature is 400 K and the temperature of the refrigerator is 300 K.

T1 = 400 K;
T2 = 300 K.
The efficiency can be calculated using the formula: η = ((T1 – T2) / T2) * 100%.
Efficiency: η = ((400 – 300) / 400) * 100% = 0.25 * 100% = 25%.
Answer: The efficiency is 25%.

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