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)`
