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A solid copper sphere (density rho and s...

A solid copper sphere (density rho and specific heat c) of radius r at an initial temperature `200K` is suspended inside a chamber whose walls are at almost `0K.` The time required for the temperature of the sphere to drop to 100K is …….

A

`72/7""(r rhoc)/(sigma)`

B

`7/72""(r rhoc)/(sigma)`

C

`27/7""(r rhoc)/(sigma)`

D

`7/27""(r rhoc)/(sigma)`

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