Informative writing- Einstein's Photoelectric effect

 Albert Einstein, a German physicist, is considered one of the greatest scientists of all times. He has contributed to the fields of general relativity, black holes, photoelectric effect, to name a few. In 1921, Einstein was awarded the Nobel Prize in physics for the discovery of the photoelectric effect.


Einstein's idea about light was revolutionary and magnificent. He gave an efficient method of irradiation. Light has some tiny group of particles known as photons. These particles consist of higher energy, which is also called the quantum of radiation. Therefore, light is made up of packets of energy or quantum of energy. Photons carry momentum and energy from the source of light by which they are emitted.


The discovery of the photoelectric effect was one of the greatest achievements of Einstein's life, for which he received the Nobel Prize. Einstein was the first to suggest that light is both a wave and a particle. This is called the wave-particle duality of light. The wave-particle duality is the fundamental concept behind quantum mechanics and the reason for the development of solar cells and electron microscopes. According to the Photoelectric effect, when a metal surface is irradiated with light of sufficient energy, it causes the electrons of the metal to eject out. So, let’s try to understand the explanation behind the Photoelectric effect.

Einstein’s Theory of Photoelectric Effect

The electrons present inside the atoms of the metal surface gain energy and start vibrating with high frequency, due to the oscillating electric field of the incident light. When the energy of incident radiation is higher than the work function of the metal, the electrons receive sufficient energy to eject out of the surface. The speed and number of the emitted electrons depend upon the color and intensity of the incident radiation, along with the time duration of incident radiation.


  • When the intensity of incident radiation is more, the electrons receive more energy and vibrate more, so an increased number of electrons are emitted out with greater average speed.

  • Incident radiation of higher frequency makes the electrons vibrate faster, thereby increasing the electron emission. Dim light normally doesn't provide the energy necessary for electron emission.


What Is the Photoelectric Effect?

When incident radiation on light having energy greater than the threshold value of metal hits the surface, the tightly bound electrons of the metal are set loose. A particle of light is called a photo. When a photon collides with electrons, it imparts the sum of its energy to it, causing the electron to eject out of the surface. The remaining energy of the photon forms a free negative charge called photoelectron.


Einstein’s Explanation of the Photoelectric Effect

  • The strength of the photoelectric current depends upon the intensity of incident radiation, and it should be higher than the threshold frequency.

  • The reverse stopping potential was the photo-current stop. It is independent of the intensity of incident radiation.

  • Photoelectric current does not occur if the frequency of the incident radiation is below the threshold frequency. A metallic strip, when exposed to light or sun, will not be able to produce the Photoelectric effect unless the frequency is greater than the threshold value.

  • The photoelectric effect is an instantaneous process. As soon as light hits the surface, the electrons of the metal come out.


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