$A$ spherical body of emissivity $e = 0.6$ placed inside a perfect black body is maintained at temperature $T$. The energy radiated per second by the body will be:

$A$ solid cylinder of length $L$ and radius $r$ is heated up to the same temperature as that of a cube of edge length $a$. If both have the same material,volume,and are allowed to cool under similar conditions,then the ratio of the amount of radiation emitted will be (Neglect radiation emitted from the flat surfaces of the cylinder).

In which of the following phenomena do heat waves travel along straight lines with the speed of light?

Heat energy is incident on the surface of a material at the rate of $1000 \ J \ min^{-1}$. If the coefficient of absorption is $0.8$ and the coefficient of reflection is $0.1$,then the amount of heat energy transmitted through the material in $5$ minutes is: (in $J$)

Regarding black body radiation,which one of the following is the $WRONG$ statement?

$A$ sphere,a cube,and a thin circular plate,all made of the same material and having the same mass,are heated to the same temperature of $200^{\circ} C$. When these are left in a room,which one reaches room temperature the fastest?