When the photon fall on surface its energy is absorbed in two ways, by the work function of metal (to kick out electron form the atom) and rest is used in the form of kinetic energy.

The total energy of the incoming photon, E_photon, must be equal to the kinetic energy of the ejected electron, KEelectron​, 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 Φ:

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 +Φ

If a photon with energy greater than E_o strikes the metal, then part of its energy is used to overcome the forces that hold the electron to the metal surface, and the excess energy appears as the kinetic energy of the ejected electron:

kinetic energy of ejected electron=

The equation in terms of the electron's kinetic energy is:

KE_electron ​=hν−Φ

Therefore, the energy required to get the electron of the electron out from the surface is hν– ϕ.

And if the electron is in the inside of a metal then it can collide with the others atom and lose its energy. If in collision it loses all its energy it does not come out.