posted by sand on .
A brick wall with a thermal emissivity of 0.8 is heated by the sun all day and is at a temperature of 25 °C in early evening. A pedestrian walking past the wall feels its warmth radiating in to the cool evening air. The wall has surface area of 5m^2. What is the total out put power of the thermal radiation emitted by the wall? Ignore radiation absorbed by the wall from surrounding bodies.