A black body radiates maximum energy at wavelength λ and its emissive power is E. Now, due to a change in the temperature of that body, it radiates maximum energy at wavelength 2λ3. At this new temperature, its emissive power will be:

For an opaque body, the relation between absorptivity α, reflectivity ρ, and transmissivity τ is:

The physical law stating that the total energy emitted per unit surface area of a black body is directly proportional to the fourth power of its absolute temperature is: