The mass of 1 litre of helium under a pressure of 2 atm and at a temperature of `27^(@)C` is

Explanation

The area of the blackbody is `A=10^(-4)m^(2)` , its temperature is `T_(1)=327(@)C=600K` . and the temperature of the enclosure is `T_(2)=27(@)C=300K` . The blackbody emits radiation at the rate of `AsigmaT_(1)^(4)` . The radiation falls on it (and gets absorbed) at the rate of `AsigmaT_(2)^(4)` .The net rate of loss of energy is `Asigma(
T_(1)^(4)-T_(2)^(4))` . The heater must supply this much of power. thus, the power needed is `Asigma(
T_(1)^(4)-T_(2)^(4))` . `=(10^(-4)m^(2)(6.0xx10^(-s)Wm^(-2)K^(-4)^(4)-(300K)^(4)]`. `=0.73W` .