Photoelectric Effect – Equation, Experiment, Work Function Explained

At the end of the article, you will know about – Photoelectric effect, equation, experiment and the work function of the effect. let’s just get started. The photoelectric effect explained by Planck’s Quantum theory in 1887.

The scientist Hertz discovered that whenever a beam of light (made of bundle packets energy called photon) of certain frequency strikes the metal surface the electrons are emitted rejected from the metal surface the phenomena is called Photoelectric effect.

  • The ejection of electrons from caesium metal is easy. It is because caesium element has the tendency to hold the electrons loosely. That is why its ionization enthalpy is very low.

Ionization enthalpy Energy required to remove an electron from the atom.

Photoelectric Effect Experiment

The whole experiment is carried out in a photoelectric cell consists of an evacuated glass tube fitted with two electrodes connected to the outer circuit with the voltage battery. The cathode is coated with the metal having low ionization enthalpy (such as Cesium). Photons of light radiation of certain frequency are allowed to strike on the cathode side. The emitted electron travels towards the anode. These are also called photoelectrons because photons are responsible for the emission of the electrons.

Experiment

Remember that

    • The kinetic energy of electrons is directly proportional to the frequency of striking Photon and it is quite independent of intensity.
    • The number of electrons is ejected per second depends upon the intensity of striking Photon, not upon their frequency.

  • A photon of light of certain minimum frequency called as threshold frequency. Threshold frequency cause emission of an electron from the metal surface. However, a photon may have large energy.
  • The different metals have the different threshold frequency

Photoelectric Effect Equation

The photoelectric effect equation can be understood easily with the help of particle nature of light. A light consists of quantum (packet) of photon this was proposed by Sir Einstein. Photon is a source of energy (E).

E =h x v

  • h= Planks Constant (6.626 x 10-34)
  • v= Frequency

Actually, the electrons are held by a nucleus of the metal atoms by a certain force called binding force. In order to escape electrons we to supply the energy to overcome the binding force. This job is performed by the photon which contains minimum energy be called as threshold energy to break down the binding energy. The threshold energy is also known as work function(W0). Now, it is the energy needed to bring about the photoelectric effect.

Equation

Under the circumstances, the extra energy is considered as the kinetic energy of the ejected electrons.

Energy(E) = Work function + kinetic energy

E=hv=hv+ 1/2m v2

Photoelectric Effect Work Function

  1. If the energy of incident Photon is <(less than)threshold energy, no electron will be emitted.
  2. If the incident Photon has the energy =(equal) to the threshold energy, the electron will just release from the metal surface.
  3. In case of the striking photon have the energy >(greater than) than threshold energy, emit electron will acquire some kinetic energy.

This all about the basics of the Photoelectric effect, equation, experiment and the work function of the effect.