 Solution

ID: past-exam-of-the-physics-b-course-of-the-university-of-cambridge/2013/paper-2/section-c/c12/ii/solution

For the ideal reversible comparison,

T_{H} = 293.15

K and the coldest air source is

268.15

K. Thus

COP_{air} = \frac{293.15}{25} = 11.73, \frac{W _{air}}{W _{direct}} = \frac{25}{293.15} = 0.0853.

A real air-source pump uses more work than this reversible lower bound, and its low-temperature performance is not specified.

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