The theory of the photoelectric effect successfully determines the reason for the radiation and the difference of energy between the incident photon and the radiated electron for the material surface. Einstein describes the radiation of energy from the surface due to the absorption of photons by “Planck’s quantum theory”. Therefore, by this theory of photoelectric effect, the radiation of light travels in the form of discrete photons in the photoelectric cell. The energy of the incident photon is equal to hv, where h is Planck’s constant and v is the frequency of the radiated light in the surface.

E=hv

What are the laws of the Photoelectric effect?

The four laws of photoelectric emission depend on the property of the radiation and absorption of energy in the material surface.

• There is no difference in the cycle time of light and the emission of electrons from the material surface.
• The frequency of the incident photon in the surface material determines the energy in the radiated electron from the surface.
• The intensity of the light incident and the number of electrons radiated from the surface is proportional to each other.
• In the photoelectric effect, there is a standard value of frequency below which the photoelectric radiation does not occur. 
• The law of photoelectric effect denotes that energy of the absorbed light is always inversely proportional to the wavelength.

Explanation of the law of the photoelectric effect

The law of the photoelectric effect denotes that the kinetic energy in the radiated electron depends on the intensity of the light in the material and the wavelength of the light in the constant cycle of time. The law of the photoelectric effect describes that the incident photon requires the energy for releasing electrons from the surface and that the kinetic energy depends on the intensity of the incident photon on the surface.

E=W+KE

hv=W+KE, therefore, KE=hv-W

From the above equation, it is clear that the kinetic energy of the radiated electron depends on the energy required to release the electron from the surface.

Who discovered the law of the photoelectric effect?

Einstein first discovered the law of photoelectric effects in 1905; however, German physicist Hertz first discovered in 1887 that reflecting UV light on the metal surface could result in sparks from the surface. Einstein discovered that the energy of the radiated electron depends on the frequency of the light and without the required threshold limit of the frequency there is no chance for the photoelectric perfect in the surface. Einstein discovered the effect of photoemission from the surface by using Planck’s constant in the photoelectric equation.

E=hv (E= energy, h=Planck’s constant, v=frequency of light)

The energy transferred by each particle of the absorbed light is directly proportional to the frequency of the light in the photoelectric effect.

Characteristics of photoelectric effects

• The law of the photoelectric effect depends on the principle of radiation and absorption theory from the surface with the help of incident energy transferred to the surface.
• The emission of the electron from the surface depends on the cut off frequency of the light and below the cut off frequency, no photoelectric effect occurs from the surface.
• Different materials have different cuts of frequency therefore, the light emission from the surface depends on the frequency of the absorbed light in the surface.
• The transfer of energy from the incident photon to the electron depends on the constant energy or work function. 

Formulation of law on external photoelectric effect

Formulation of the law of the photoelectric effect depends on the threshold frequency and at the threshold, frequency electrons are released from the surface without having any kinetic energy, therefore the energy of the photon at threshold frequency is equal to the work function in the Kinetic energy equation. 

fc=ϕ/h (ϕ= work function, h=frequency, fc=cut-off frequency)

Cut-off frequency in the Einstein photoelectric equation depends on the work function in the radiation process. Therefore, when the work function is large, then the incident photon requires more energy to emit electrons from the surface.

Theory of photoelectric effect

Planck’s quantum theory of photoelectric effect suggests the process of photoelectric emission from the surface of the material due to absorption of energy in the surface. Planck’s quantum theory describes that light is the small package of quantum energy in terms of photons. Therefore, the maximum kinetic energy of an electron is directly proportional to the energy of the incident photon and inversely proportional to the wavelength. 

Conclusion

The above study indicates that the law of the photoelectric effect helps to determine the required kinetic energy for the successful emission of electrons from the surface of the photoelectric cell. Work function depends on the frequency of the light reflected on the surface. Energy absorbed through the surface requires a high frequency to emit electrons from the surface.