A black coloured solid sphere of radius $R$ and mass $M$ is inside a cavity with vacuum inside. The walls of the cavity are maintained at temperature $T_0$. The initial temperature of the sphere is $3T_0$. If the specific heat of the material of the sphere varies as $\alpha T^3$ per unit mass with the temperature $T$ of the sphere, where $\alpha $ is a constant, then the time taken for the sphere to cool down to temperature $2T_0$ will be ( $\sigma $ is Stefan Boltzmann constant)
$\frac{{M\alpha }}{{4\pi {R^2}\sigma }}\,\ln \left( {\frac{3}{2}} \right)$
$\frac{{M\alpha }}{{4\pi {R^2}\sigma }}\,\ln \left( {\frac{16}{3}} \right)$
$\frac{{M\alpha }}{{16\pi {R^2}\sigma }}\,\ln \left( {\frac{16}{3}} \right)$
$\frac{{M\alpha }}{{16\pi {R^2}\sigma }}\,\ln \left( {\frac{3}{2}} \right)$
Are rate of heat emission and rate of cooling same ? Explain this.
Equal masses of two liquids are filled in two similar calorimeters. The rate of cooling will
A solid sphere and a hollow sphere of the same material and size are heated to the same temperature and allowed to cool in the same surroundings. If the temperature difference between each sphere and its surroundings is $T$, then
A cup of tea cools from ${80^0}C$ to ${60^o}C$ in one minute. The ambient temperature is ${30^o}C$. In cooling from ${60^o}C$ to ${50^o}C$ it will take ....... $\sec$
A cup of coffee cools from $90^{\circ} \mathrm{C}$ to $80^{\circ} \mathrm{C}$ in $\mathrm{t}$ minutes, when the room temperature is $20^{\circ} \mathrm{C}$. The time taken by a similar cup of coffee to cool from $80^{\circ} \mathrm{C}$ to $60^{\circ} \mathrm{C}$ at a room temperature same at $20^{\circ} \mathrm{C}$ is :