A copper sphere is suspended in an evacuated chamber maintained at 300 K. The sphere is maintained at a constant temperature of 500 K by heating it electrically. A total of 210 W of electric power is neede to do it. When the surface of the copper sphere is completely blackened, 700 W is needed to maintain the same temperature of the sphere. The emissivity of copper is _______ xx10^(-1)

A copper sphere is suspended in an evacuated chamber maintained at 300

1.	A copper sphere is suspended in an evacuated chamber maintained at 300 K. The sphere is maintained at a constant temperature of 500 K by heating it electrically. A total of 210 W of electric power is neede to do it. When the surface of the copper sphere is completely blackened, 700 W is needed to maintain the same temperature of the sphere. The emissivity of copper is _______ xx10^(-1)
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