Einstein's Explanation Of Photoelectric Effect - A Complete Guide

Albert Einstein, one of the greatest physicists, contributed his inevitable works and proposed many theories in different fields of physics like the special theory of relativity, concepts of the black hole, photoelectric effect, Einstein quantum theory, Einstein-Maxwell equation, many more topics and some other assumptions. His instinct on the theories never fails. In any field, the Albert Einstein equation plays a prominent role and the Einstein photoelectric equation can be considered as the best achievement of his work. In 1921, he received the Nobel Prize in Physics for his work Einstein theory of photoelectric effect.

Let us discuss the explanation of the photoelectric equation, learn the concept of quantisation and try to derive Einstein photoelectric equation. Along with this, we will also see some explanation on other terms like threshold energy (threshold meaning), Work function and Stopping potential, instinct meaning, instance meaning, threshold meaning, emit meaning, Einstein photoelectric equation, spontaneous emission, quantisation, einstein photoemission meaning, the meaning of assumption, explanation of the theory of relativity, electric effect, threshold frequency formula, and kinetic meaning.

What is Einstein's explanation about the photoelectric effect?

The photoelectric effect is an effect caused when the light is incident on the surface of any metal; the electrons get emitted from the surface of the metal. For instance, the incident light should have some sufficient frequency to eject the electron from the surface of the metal. Initially, this photoelectric effect was explained by a physicist named Heinrich Hertz in the year 1887 and later it was preceded by Lenard in the year 1902. But, Maxwell’s theory of electromagnetic waves of light was not able to explain both the observation of Hertz and Lenard in the photoelectric effect. Comparing the photoelectric effect and wave theory of light, there are some failures of wave theory which made Einstein explain the photoelectric effect with a concept of light as a particle. Let us see some of the failures of wave theory.

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Failures in Wave theory:

• Wave theory explains that Energy is distributed across the wavefront uniformly. It depends only one the light beam’s intensity. This gives the inference that kinetic energy K.E increases with the intensity of the light beam and Kinetic energy have its dependence on the intensity of the light. But this concept is not exactly correct, because kinetic energy is not dependent on light intensity.
• According to the theory, a Light beam with any frequency or wavelength can emit electrons from the surface of the metal. But this statement also cannot be proved because for ejecting electrons from the surface of the metal, minimum frequency is required.
• Also, wave theory concludes that electron emission is based on the intensity of light, as the energy distribution depends on the intensity of light. Finally, this idea also has a flaw, as the electron’s spontaneous emission is independent of the intensity of light.

Einstein’s Explanation of Photoelectric effect:

Now, let us elaborate and explain the Einstein photoelectric equation. Photoelectric effect is explained by Einstein in a different perspective by resolving all the failures in wave theory. He utilized Planck's ideology of particle nature of light in this photo electric effect. Also, by photoelectric effect, Einstein proved that light also has particle nature. Now, the energy carried by each unique particle of light is only dependent on the frequency of light, not the intensity of light. This energy carried by each and unique particle of light is also known as the quanta or photon. This can be written as E = hν, where h is Planck’s constant which is equal to 6.626 x 10-34 J Hz-1 and ν is frequency of light.

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According to Einstein, All of the energy of the incident photon is transferred from photon to ejected electron. Some part of the energy of the incident photon is used up to remove the electron from the surface of the metal and the balance part of the energy of the incident photon is converted into the kinetic energy of the ejecting electron. And the electron will have the maximum kinetic energy.

The laws of photoelectric emission:

• There is a minimum cutoff frequency required for emission of electrons. Below this frequency, no electron emission occurs
• The total number of emitted electrons increases with the intensity of incident light
• Kinetic energy of the electrons emitted is dependent on the frequency of light and independent of intensity of light
• There are zero time lags between the incidence of the light beam and electron emission.

Explanation of scientific terms in Photoelectric effect:

Threshold Frequency:

The minimum frequency of the given incident light beam which is required for the emission of electrons from the surface of the metal is known as Threshold frequency.

Work Function:

The Energy required in the removal of the electron from the surface of the metal is known as Work Function.

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Stopping potential:

The required potential to stop the emission of the electron from the surface of the metal is known as stopping potential.

Let us derive Einstein’s photoelectric equation mathematically and this can be written as

Energy of photon = Energy required to remove the electron from the surface of the metal (W) + Maximum Kinetic energy of the electron which is ejected from the surface of the metal.

E = W +K.E

hν = W +K.E

K.E = hν -W

At the point of threshold frequency, the electron does not possess any kinetic energy. At the same time, below the point of threshold frequency, the electron will not get ejected from the surface of the metal i.e. no emission of electrons occurs. Thus, the photon energy with threshold frequency will be equal to the Work function of the metal and this can be also written as

W= hν_o

Therefore, for maximum kinetic energy, the equation can be written as

K.E max= ½ (mv²) = hν - hν_o = h (ν - ν_o) >>>> 1

K.E max is the maximum kinetic energy of the electron which is ejected from the surface of the metal.

Now, the stopping potential Eν_o= ½ (mv_max²) >>>> 2

Equating both the equations no. 1 and 2, we get

Eν_o= ½ (mv_max²) = h (ν - ν_o)

Therefore, the Photoelectric effect mathematical expression is inferred from the above equation.

From this article, we learnt about the Einstein photoelectric effect experiment and photoelectric definition. Let us see some FAQs related to Albert Einstein’s photoelectric effect.
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