The coefficient of absorption $(a)$ and the coefficient of reflection $(r)$ of a thin uniform plate are $0.77$ and $0.17$ respectively. If $250 \ kcal$ of heat is incident on the surface of the plate,the quantity of heat transmitted $(t)$ is: (in $kcal$)

For a perfect black body,the absorption coefficient is

Two identical objects $A$ and $B$ are at temperatures $T_A$ and $T_B$ respectively. Both objects are placed in a room with perfectly absorbing walls maintained at temperature $T$ $(T_A > T > T_B)$. The objects $A$ and $B$ attain temperature $T$ eventually. Which one of the following is the correct statement?

$A$ body is in thermal equilibrium with its surroundings. This is because .....

Three identical metal spheres (of same surface area) have red,black,and white colors and they are heated up to the same temperature. They are allowed to cool. Arrange them from maximum rate of cooling to minimum rate of cooling.

Compared to a white-skinned person,what does a dark-skinned person experience?