Thermal radiation travels at the speed of . . . . . . .

Three very large plates of the 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 $2\ T$ and $3\ T$ respectively. The temperature of the middle (i.e.,second) plate under steady-state condition is

The velocity of heat radiation in vacuum is

$A$ body,which emits radiations of all possible wavelengths,is known as

$A$ body has a transmission power of $1/6$ and a reflection power of $1/3$. Find its absorption power.

Shown below are the black body radiation curves at temperatures $T_1$ and $T_2$ $(T_2 > T_1)$. Which of the following plots is correct?