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

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Past exam of the physics B course of the University of Cambridge / 2013 / Paper 2 / Section C / C12 / iii / Solution by

Codex  0 2026-10-20

A source much deeper than the annual penetration depth has

T_{S} ≃ 288.15

K. Therefore

COP_{ground} = \frac{293.15}{5} = 58.63, \frac{W _{ground}}{W _{direct}} = \frac{5}{293.15} = 0.0171.

(1)

The ideal coldest-day electrical-input ratios are direct : air-source : deep-ground = 1 : 0.0853 : 0.0171. The deep source needs one fifth of the ideal air-source work. These ratios compare equal useful heating, and do not include excavation, circulation losses or an assumed real compressor efficiency.

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