Einstein's Explanation of 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.

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.

Planck’s Theory and the Photoelectric Effect

Planck's theory was expanded by Einstein in 1905 to explain the photoelectric effect, which is the release of electrons by metal when exposed to light or high photons. The kinetic energy of the released electrons is determined by the frequency of radiation v, not their intensity; for a certain metal, there is a frequency 0, below which no electrons are released. In addition, emissions occur as soon as the light strikes; there is no apparent delay. These effects can be explained by two assumptions, according to Einstein: light is made up of corpuscles or photons, whose power is determined by Planck's equation, and a single metal atom can absorb a whole photon or anything. Albert Einstein proposed that light beats were not a wave propagating the atmosphere, but massive packets of different energies were known as photons, since low-frequency beams could not produce the energy needed to produce photoelectrons, as light energy from continuous waves .

Light beam photons with a different intensity, called photon energy, are equal to the frequency of light. When the electron inside an active substance absorbs the photon energy and gains more energy than its binding force, it is more likely to be released from the imaging process. An electron cannot emerge from an object when the photon energy is too low. Because increasing the intensity of low-intensity light will only increase the number of low-energy photons, no single photon with sufficient electron output will be produced. In addition, the electron energy released is determined only by the individual photon energy, not the intensity of the incoming light of a particular frequency.

Photoemission can occur in any object, although it is most commonly seen in metals and other conductors. This is because the process creates a cost imbalance, which, if not measured by the current flow, causes the barrier to rise until the discharge is completely exhausted. Because non conductive oxide ports on metal surfaces raise the energy barrier in image extraction, many functional investigations and devices based on the effect of electric photography require clean metal surfaces in the extracted tubes. The vacuum also facilitates electron microscopy by preventing gasses from interfering with electron passage between electrodes.

Einstein’s Equation of the Photoelectric Effect 

According to the Einstein-Planck relation,Einstein explained the photoelectric effect based on Planck’s quantum theory, according to which, light radiation travels in the form of discrete photons. The energy photon is hv , where h is constant and v is the frequency of light .

 E = hν …(1)

Where 'h' is Planck's constant, and 'ν' is the frequency of the emitted radiation.

From the experiments of the Photoelectric effect, it is found that no electron emission occurs if the incident radiation has a frequency less than the threshold frequency. From the equation, you can know that energy is directly related to frequency, and this also explains the instantaneous nature of electron emissions.

When the photoelectron comes out of the metallic surface, it will be converted to purely kinetic energy as there is no electric field outside the surface. The quantum energy imparted by the photons is partly used by the electron to overcome the molecular attraction of the surface.

So, the kinetic energy of a photoelectron is = (energy imparted by photon) - (energy used to come out of the surface).

This energy is constant for a surface, and it is denoted by Φ. This is called the work function of a surface and is constant for a given material. Thus the equation is given as,

K.E. = hν – Φ …(2)

This is Einstein's photoelectric equation.

The same case happens with the photoelectrons. The electrons need minimum threshold energy to get ejected out of the surface. When electrons are imparted with a threshold frequency (v0), they acquire enough energy to eject out of the surface. If the electron gets energy equal to threshold frequency, its kinetic energy becomes zero after coming out of the surface. Using this, we have

hv0 – Φ = 0 or hv0 = Φ ….(3)

Using this in equation (2), we get K.E. = hν – hν0

or K.E. = h(ν – v0)

Also, v0 is the Stopping Potential, So

K.E. (max) = eV0; and putting this in equation (3), we have:

eV0 = h (ν – v0) ……(4)

Using this equation; the value of 'h' is calculated for the Photoelectric effect. The values obtained by this equation are in congruence with actual values, thus proving Einstein's explanation for the Photoelectric effect.

How does the Photoelectric Effect function?

In 1905, Einstein introduced the theory of electric shock based on Max Planck's theory that light is composed of tiny energy packets known as photons or luminous quanta. Each packet contains a hv of power equal to the frequency v of the corresponding electromagnetic wave. Planck constant is named after proportionality constant h.

Niels Bohr of Denmark made a significant contribution to this field when he applied quantum theory to the atomic spectra in 1913. Since the middle of the nineteenth century, the spectrum of light emitted by atoms of gas has been thoroughly studied. At low pressure, it was discovered that radiation from gaseous atoms contained a set of different wavelengths. On the other hand, rays from solid solids disperse between continuous wavelengths. A line spectrum is a set of defined wavelengths emitted by gas atoms, as the emissions (light) emitted are made up of a series of clear lines.

Experimental physicists faced a major challenge in the late 1800's. James Clerk Maxwell, a mathematician, published his theory of electromagnetism hypothesis in 1865, stating that electricity and the magnetic field both travel through space like light waves. The examiners then went out to obtain a definite confirmation of Maxwell's theories, which, at least in theory, accurately described the characteristics of light.

The Electromagnetic effect

The distribution of electronic conditions in terms of strength and pressure — the structure of the solid electronic band — determines the electronic characteristics of the ordered, shiny solid materials. The theoretical imitation of solid-state photoemission suggests that this distribution is kept to a large extent electromagnetic effect.

The internal photoelectric effect is a direct optical transition between a busy and impersonal electronic environment with a multitude of materials. Quantum-mechanical selection principles for dipole moments change this situation. A second electron emission, or so-called Auger effect, can emerge from a hole left by the electron, even if the primary photoelectron does not come out of the material. This process stimulates the pens to solid molecular targets, which can be seen as satellite lines in the electron reserve.

Electron scattering at the top, with other electrons dispersed due to interactions with other solid elements. Electrons from the deepest part of the material are more likely to collide and come out at different speeds and speeds. Their non-mechanical mechanism is a universal curve determined by electron energy.

Conclusion

When high-energy light travels through a threshold that strikes a metal surface, the electron-bound electron is released. When a photon collides with an electron, it uses some of its energy to release the electron from the metal. The remaining energy of the photon is transferred to the negative charge now known as the photoelectron. This is the photoelectric effect.