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A black ened metal sphere of radius 7 cm...

A black ened metal sphere of radius 7 cm is encllosed in as evacuated chamber maintained at a temperature of `27^(@)C`. At what rate must energy be supplied to the sphere so as to keep its temperature constant at `127^(@)C` ?
`sigma=5.7xx10^(-8) W m^(-2) K^(-4)`.

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