An electric bar heater is rated at and is switched on for hours a day

PHYSICS · Multi-part · Fermi University Physics · Thermal, Statistical & Complex Systems · The laws of thermodynamics · The laws of thermodynamics

Thermal Physics, Ch The second law, entropy and irreversibility

Problem

An electric bar heater is rated at

2.0\,\mathrm{kW}

and is switched on for

8.0

hours a day. Its glowing element is held by the electricity supply at about

1000\,\mathrm{K}

and passes its heat to the air of the room, which stays at

293\,\mathrm{K}

. Model both the element and the room air as reservoirs at those fixed temperatures, and take the room air at

293\,\mathrm{K}

as the coldest body available. Consider only the heat flow from the element to the room. ((a)) Estimate the heat delivered to the room in one day. ((b)) Estimate the entropy created by this heat flow in one day. ((c)) Estimate the work lost in one day, and express it as a fraction of the heat delivered.

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