An electric heater supplies of electrical work to of water initially at contained in…

PHYSICS · Subjective · CBSE · Physics · Thermodynamics · Thermodynamics

Problem

An electric heater supplies

1000\,\text{J}

of electrical work to

1.0\,\text{kg}

of water initially at

298\,\text{K}

contained in an open beaker kept in a room whose air is also at

298\,\text{K}

. During the heating,

600\,\text{J}

of heat is transferred from the water to the room. After the heater is switched off, the water eventually cools back to

298\,\text{K}

, returning to its initial state. (Specific heat capacity of water is

4200\,\text{J\,kg}^{-1}\text{K}^{-1}

and may be taken as constant.) (a) For the heating stage, calculate the entropy change of the water and of the room separately. (b) For the subsequent cooling stage, calculate again the entropy change of the water and of the room. (c) Determine the net change in entropy of the universe for the complete cycle (heating followed by cooling). (d) Based on your result, comment on the feasibility of constructing a device that converts all electrical work directly into mechanical work in a cyclic process without any net change in the entropy of the universe.

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