Physics

Problem

An electric heater is used in a room of total wall area

137\,\text{m}^2

to maintain a temperature of

+20^{\circ}\text{C}

inside it, when the outside temperature is

-10^{\circ}\text{C}

. The walls have three different layers materials. The innermost layer is of wood of thickness

2.5\,\text{cm}

, the middle layer is of cement of thickness

1.0\,\text{cm}

and the outermost layer is of brick of thickness

25.0\,\text{cm}

. Find the power (in kW) of the electric heater. Assume that there is no heat loss through the floor and the ceiling. The thermal conductivities of wood, cement and brick are

0.125

1.5

and

1.0\,\text{W/m}^{\circ}\text{C}

respectively.

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