Intensity is energy per unit time per unit area which is directly proportional to the no of photon falling in unit area in unit time. The formula for intensity is articulated by,

Where I is the intensity, E/T is the energy per unit time, n is the no. of photons and A is the area of cross section.

Therefore, if intensity is increased, the number of photons falling per unit area per unit time is also increased. Therefore, the no. of photons emitted by the source in unit time increases.

And increase in intensity results in increase in energy per unit time. And there is increase in total energy of photons emitted per unit time as number of photons increase.

Photons have kinetic energy which depends upon the frequency of photons.

We can analyze the frequency relationship with the kinetic energy using the law of conservation of energy. The total energy of the incoming photon, E_photon​, must be equal to the kinetic energy of the ejected electron, KE_electron​, plus the energy required to eject the electron from the metal. The energy required to free the electron from a particular metal is called the metal's work function, which is represented by the symbol :

We can now write the kinetic energy of the photon in terms of the light frequency using Planck's equation:

E_photon = hν = KE_electron ​+

Intensity increase does not change the nature of light, i.e. its frequency. Hence, kinetic energy of single photon is constant.

If there is no increase in kinetic energy, velocity does not change at all.