A copper sphere is suspended in an evacuated chamber maintained at `300 K`. The sphere is mantained
Channel: Doubtnut
Date: 2020-04-12

A copper sphere is suspended in an evacuated chamber maintained at `300 K`. The sphere is mantained at a constant temperature of `500 K` by heating it electrically. A total of `300 W` of electric power is needed to do it. When half of the surface of the copper sphere is completely blackened, `600W` is needed to maintain the same temperature of the the sphere. Calculate the emissivity of copper.