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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 …….

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`H=4 pi sigma r^(2) (T^(4)-0)=4/3 pi r^(3) rho C-(dT)/(dt)`
`dt=-(rho rC)/(3 sigma) int_(200)^(100)(dT)/(T^(4))=(7 rho r C)/(72 sigma)xx10^(6)s`
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