If a piece of metal is heated to temperature $\theta$ and then allowed to cool in a room which is at temperature ${\theta }_0$ the graph between the temperature $T$ of the metal and time $t$ will be closest to: 

Three very large plates of same area are kept parallel and close to each other. They are considered as ideal black surfaces and have very high thermal conductivity. The first and third plates are maintained at temperatures 2T and 3T respectively. The temperature of the middle (i.e. second) plate under steady state condition is

Two rectangular blocks, having identical dimensions, can be arranged either in the configuration $\mathrm{I}$ or in the configuration $\mathrm{II}$ as shown in the figure. One of the blocks has thermal conductivity $k$ and the other $2k$. The temperature difference between the ends along the $x$-axis is the same in both configurations. It takes $9 \mathrm{s}$ to transport a certain amount of heat from the hot end to the cold end in the configuration $\mathrm{I}$. The time to transport the same amount of heat in the configuration $\mathrm{II}$ is:

Parallel rays of light of intensity, $I=912 \mathrm{W} {\mathrm{m}}^{-1}$ are incident on a spherical blackbody kept in surroundings of temperature $300 \mathrm{K}$. Take Stefan-Boltzmann's constant, $\sigma =5.7\times {10}^{-8} \mathrm{W} {\mathrm{m}}^{-2} {\mathrm{K}}^{-4}$ and assume that the energy exchange with the surroundings is only through radiation. The final steady-state temperature of the blackbody is close to,

A composite block is made of slabs $A,B,C,D$ and $E$ of different thermal conductivities (given in terms of a constant $K$) and sizes (given in terms of length, $L$) as shown in the figure. All slabs are of same width.