# In the photoelectric effect, why is the kinetic energy of the electrons independent of the intensity of light?

Einstein was the first to explain photoelectric effect. Photoelectric effect is a phenomenon in which electrons are released from the metal’s surface when light falls at a certain frequency. No electrons will be emitted if the light falls below a certain frequency. However, electrons will still be emitted if the light is above a certain frequency, even though it may not be very intense.

This phenomenon has predicted the particle nature light. Photons are particles that make up light. The above mentioned problems can be easily solved. Imagine that we shine a low-frequency light with a high intensity, and nothing happens. The electron will only interact with one photon no matter how intense the light is, so frequency is the key component of photoelectric effect.

To emit electrons from the metal surface, they need energy. This energy is called work function (W). It depends on the metal. Photons interact with electrons. If the photon has enough energy to absorb the energy, the electron can escape the metal. The electrons cannot be removed by a photon with an energy lower than the work function.

If light of frequency (f) is incident upon a metal surface with a work function ( w), then the maximum kinetic energie of the emitted electron will be

K.Emax=hf- w

The maximum kinetic energies of the emitted electrons would be determined by their kinetic energy. The photon’s energy would equal the energy of its electron. However, the K.E calculation uses the work function to subtract the photon’s energy from the atom. This determines how much energy is required to expel an electron.

If the intensity of light above the work function is increased, the photon interaction would increase and emit more electrons. However, the maximum kinetic energy would not change since the energy of the photon will remain the same. The opposite would happen. If the frequency or energy is increased, the work function would not change but the energy would be higher and the max kinetic energy comparatively would be greater (you can see the explanation in the K.E formula).