A room at `20^@C` is heated by a heater of resistence 20 ohm connected to 200 VV mains. The temperature is uniform throughout the room and the heati s transmitted through a glass window of area `1m^2` and thickness 0.2 cm. Calculate the temperature outside. Thermal conductivity of glass is `0.2 cal//mC^@` s and mechanical equivalent of heat is `4.2 J//cal`.

Answer

15.24

Explanation

Power produced by heater = rate of heat flow through window `therefore(V^(2))/(R)=("Tem perature difference")/("Them alresistance")=(20-theta)/((l//KA))thereforetheta=20-(V^(2)l)/(KAR)`
Substituting the values we have, `theta=20-((200)^(2)(0.2xx10^(-2)))/((0.2xx4.2)(1)(20))=15.24^(@)C`