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`.

Explanation

Rate of heat generation is
`V^(2)/(R)=(200)^(2)/(20)=2xx10^(3)W`
If outside temperature is T we use
`2xx10^(3)=(0.2xx4.2xx1)/(0.2xx10^(-2))(20-T)`
`impliesT=20-4.76=15.24^(@)C`