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 …….

Answer

A

Explanation

Energy radiated per second ` = sigma AT^(4)`
`Ssigmamc((-dT)/(dt))=sigmaAT^(4)underset(0)overset(t)intdt=((-dT)/(sigmaA))=underset(200)overset(100)intT^(4)dT`
`t =(mc)/(3 sigmaA)[(1)/((100)^(3))-(1)/((200)^(3))],=(7mcxx10^(-6))/(24sigmaA)=1.71rhorc` .