A designer wishes to extract the maximum useful work from a heat source at while…

PHYSICS · Multi-part · A Level · Physics · Engineering physics · Engineering physics

Problem

A designer wishes to extract the maximum useful work from a heat source at

T_H = 700\,\text{K}

while discharging heat to the environment at

T_C = 350\,\text{K}

. In each cycle the source can supply at most

4000\,\text{J}

of heat. Consider the following points. (i) Derive an expression for the maximum theoretical work obtainable per cycle and evaluate its numerical value for the given data. (ii) The designer claims to have built an engine that produces

3000\,\text{J}

of work per cycle while rejecting

1000\,\text{J}

of heat to the

350\,\text{K}

sink. Determine whether this claim violates the second law and give reasons. (iii) If the claim in part (ii) were true, describe how such an engine could be combined with other standard devices to create a perpetual-motion machine of the second kind.

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