FEELING VERY COLD-SWITCH ON THE "HEATER"

An electric heater is used in a room of total wall area of $137m^{2}$ to maintain a temperature of 20 centigrade inside it, when the outside temperature is -10 centigrade. The walls have three different materials.The innermost layer is of wood of thickness 2.5cm, the middle layer is of cement of thickness 1cm and the outermost layer is of brick of thickness 25cm .

The power of the electric heater is given by $a \times 1000$

Find the value of a

1.ASSUME THAT THERE IS NO HEAT LOSS THROUGH FLOOR AND THE CEILINGS.

2.THERMAL CONDUCTIVITIES OF WOOD,CEMENT AND BRICK ARE 0.12,1.5 AND 1.0 watt/m/centigrade RESPECTIVELY.