The concrete wall of a building is 0.14 m thick. Thetemperature inside the building is 22°C, while the temperatureoutside is 0.0°C. Heat is conducted through the wall. When thebuilding is unheated, the inside temperature falls to 0.0°C,and heat conduction ceases. However, the wall does emit radiantenergy when its temperature is 0.0°C. The radiant energyemitted per second per square meter is the same as the heat lostper second per square meter due to conduction. What is the emissivity of the wall?