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A copper sphere is suspended in an evacu...

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.

A

`(1)/(4)`

B

`(1)/(3)`

C

`(1)/(2)`

D

`(1)/(5)`

Text Solution

Verified by Experts

The correct Answer is:
B
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