  # Photo Electric Effect of Light and Wave Theory of Light

Physics

## formula

### Introduction to maximum kinetic energy

What happens when a light of is incident on a metal? Let us say that the frequency of the light is more than threshold frequency. Hence we know that electrons may emit from the metal surface. But we haven't covered the further story. Will the electron come out for sure? No. There is no surity of ejection of the electron. Why?
Let us understand this. When a light is incident on the metal, the electrons may or may not acquire the energy of the light. What if an electron acquires all the energy of the light. This electron now has capability to come out. But electrons oscillate continously.  So this electron may collide with other electrons. Some energy will be lost in this process. Hence the electrons which are on the surface of the metal and headed out of the metal surface will come out.

## formula

### Formula for maximum kinetic energy

Let us say a metal is irradiated with a photon of frequency . Let this frequency will be equal to the threshold frequency of light. Let the work function of the metal be . The energy of the photon will be
As we know, some of the electrons may come out of the metal surface. What will be the energy of this photoelectron ejected?
Zero. why?
• Because the energy given to the photoelectron is spent to overcome the work function of the metal.
• What if the light of threshold frequency is replaced with light of frequency more than the threshold frequency?Photoelectrons will emit in this case also. What will be their energy? Some amount of the energy will be lost to overcome the work function of the metal. The rest of the energy may be spent in the collision with other electrons.And the energy still left after this process is converted into kinetic energy of the electron.
• Let us say some of the electrons don't lose this extra energy. These electrons will come out with maximum kinetic energy. What will this energy be?
• It will be the energy of the photon minus the work function. Or

## example

### Example on maximum velocity of photoelectron

then The work function of a metal surface is 1 eV. A light of wavelength 3000 is incident on it. The maximum velocity of the photoelectrons is found as:The maximum K.E with which electrons comes out,