The spectrum of black body radiation is a

For athermanous substances,the coefficient of transmission is

$A$ 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?

Three objects colored black,gray,and white can withstand hostile conditions up to $2800\,^oC$. These objects are thrown into a furnace where each of them attains a temperature of $2000\,^oC$. Which object will glow brightest?

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

$A$ certain substance emits only the wavelengths ${\lambda _1}, {\lambda _2}, {\lambda _3}$ and ${\lambda _4}$ when it is at a high temperature. When this substance is at a colder temperature,it will absorb only the following wavelengths: