MCQ
A solid copper sphere (density $\rho $ and specific heat capacity $c$ ) of radius $r$ at an initial temperature $200K$ is suspended inside a chamber whose walls are at almost $0K$ . The time required (in $\mu s$) for the temperature of the sphere to drop to $100\, K$ is
- A$\frac{{72}}{7}\frac{{r\rho c}}{\sigma }$
- ✓$\frac{7}{{72}}\frac{{r\rho c}}{\sigma }$
- C$\frac{{27}}{7}\frac{{r\rho c}}{\sigma }$
- D$\frac{7}{{27}}\frac{{r\rho c}}{\sigma }$
