Question

Define intensity of radiation on the basis of photon picture of light. Write its S.I. unit.

Answer 1

The intensity of radiation is defined as the energy associated with photons emitted from a unit surface area in unit time. Its S.I unit is joule/meter2second.

Answer 2

The intensity of radiation refers to the energy associated with the photons emitted from a unit surface area in unit time.

• In other words, it is the number of photons falling per unit area in unit time.

• Therefore in the photon picture, if no. of photons increases then the intensity of light increases.

• The S.I. unit of intensity of radiation is Watt per Steradian (Wsr⁻¹).