Question

In the wave picture of light , intensity of light is determined by square of the amplitude of wave. what determine the intensity of light in the photon picture of light ?

Answer 1

The photon density, that is the no. of photons per unit volume at a given point determines the intensity of light in the photon picture of light.

The intensity of a wave(carrier of energy) is defined as the energy crossing per unit area per second$\frac{\left(Power\right)}{Area}$

The intensity of a particle(Photon, quantum of energy) is defined as the flux of no. of particles per second(means no. of photons passing per area per time). So in the photon picture of light if no. of photons increases then the intensity of light increases.

the photon density n and intensity I related to each other by the relationship :

n =$\frac{I}{h\times c\times \nu }$

where, h is the Planck's constant, c is the speed of light and $\nu$ is the frequency of incident light