Q 1--> The total area of the walls of a room is 137 m2. An electric heater is used to maintain the temperature inside the room at + 200C , while the outside temperature is -100C. Walls are made of three layers of different materials. The innermost layer is made of wood 2.5 cm thick middle layer is made of cement 1 cm thick and outermost layter is made of bricks 25 cm thick. What will be the power of electric heater? Assume that there is no loss of heat from roof and floor. The coeff. of thermal conductivity of wood , cement and bricks are 0.125, 1.5 and 1 Watt/ m 0C respectively.Answer --> 9000 wattQ 2--> Atungsten heater wire of 1 m is rated at 3 KW m-1 and 5.0 * 10-4 m in diameter. It is embedded along the axis of a ceramic cylinder of diameter 0.12 m. When operating at the rated power, the wire is at 1500 0 C; the outside of the cylinder is at 200C. Find the thermal conductivity of the ceramicAnswer --> 1.77 J s-1 K -1 Answer the problem step by step

Hrishant Goswami , 10 Years ago

Grade 10