Question

What is the photoelectric effect? Write any three laws of the photoelectric effect. Explain these laws by Einstein’s equation of the photoelectric effect.

Answer 1

In this question we have been asked to define what is the photoelectric effect and state its three laws. We have also been asked to explain these laws by Einstein’s equation of the photoelectric effect. Therefore, to answer this question we shall discuss the photoelectric effect and its laws. We know that the photoelectric effect refers to what happens to an electron that is emitted and has absorbed electromagnetic radiation.

Formula Used: ${{E}_{i}}=h{{\mu }_{o}}+KE$
Where,
${{E}_{i}}$ is the energy of the incident photon
${{\mu }_{o}}$ is the threshold frequency
KE is the kinetic energy

Complete step by step solution:
We know that electrons are emitted from a surface of a metal when the light of a certain frequency hits the metal surface. This phenomenon is known as the photoelectric effect. The emitted electrons are called photoelectrons.
The three laws of the photoelectric effect are as follows;

1. The emission of electrons from the surface stops after a certain frequency known as the threshold frequency.
2. The number of electrons that are emitted from the surface is directly proportional to the intensity of the incident light.
3. Kinetic energy of the emitted electrons depends on the frequency of the incident light and is independent of its intensity.
   Einstein assumed the nature of light to be a particle instead of a wave. The energy carried by each particle of light is dependent on its frequency. Einstein said that as light consists of these particles or photons when a photon hits a metal surface, all the energy carried by the photon is transferred to the electron. This energy is used by the electron to remove itself from the metal surface and the rest of the energy after emission is given out as kinetic energy.
   The above statements by Einstein can be written as,
   $E=h\mu$
   Where $\mu$ is the frequency of incident light
   Also,
   ${{E}_{i}}=h{{\mu }_{o}}+KE$
   Where ${{\mu }_{o}}$ is the threshold frequency.

Note: The laws of photoelectric effects are based on the shortcomings of Maxwell's electromagnetic theory of light, which assumes light to be in the waveform. Therefore, using the particle nature of light Einstein explained the photoelectric effect. The photoelectric effect was first documented by Heinrich Hertz. Since he couldn’t explain the photoelectric effect using Maxwell's theory, his concept failed.