December 5, 2019

The wave nature of radiation suggests that energy is emitted or absorbed continuously as an electromagnetic wave. There were also mysteriously associated with light. In 1887, during Hert’s electromagnetic wave experiment he discovered the photoelectric effect. When light struck a metal surface, some electrons near the surface absorbed enough energy to overcome the attraction of the positive ions in the metal and escape into the surrounding space. This phenomenon was explained as the photoelectric effect.

So, the phenomenon of emission of electron from a metal surface when the light of suitable radiation is incident on it is called photoelectric emission. This effect has numerous practical applications.To escape from the surface, the electron must absorb enough energy from the incident radiations to overcome the attraction of positive ions in the material of the surface. One of the important terms for photoelectric emission is work function. The work function is the minimum of the energy required to remove the electron from a metal surface. For the emission of electron from the metal surface the work function must be fewer. As the work function of alkali metal is less they are used for photoelectric emission.

After, a certain point there will be no photoelectric emission. The minimum frequency required to eject the electron from the metal surface is called threshold frequency.

These results are hard to understand on the basis of classical physics. So in 1905 Albert einstein gave correct analysis on the photoelectric effect. Einstein postulated that a beam of light consists of small packages of energy called photon or quanta. Photoelectric emission has a lot of application as-

The photoelectric effect is often used in a burglar alarm. A beam of light is allowed to fall on the photoelectric cell this keeps the bell circuit open. When a burglar enters the premises, the ultraviolet rays fall on the photoelectric cell are blocked and the alarm gets switch on.

The photoelectric cell is used in making night vision scopes.

It is used in television cameras.

The photoelectric effect is used for switching on and off of street light.

Due to the above reasons, we can say that the photoelectric effect has become one of the greatest findings of the scientist.

Prepared By: Isha Dev, Moonlight Secondary School Kumaripati, Lalitpur.