The photoelectric effect is a physical phenomenon that occurs when a metal surface is struck by light of a specific frequency. Heinrich Hertz discovered this phenomenon in 1887, and Lenard confirmed it in 1902. Still, there were a few anomalies since Maxwell’s electromagnetic wave theory of light could not explain the photoelectric effect.

Einstein took advantage of Planck’s concept of light as a particle to address the previously occurring problem with the photoelectric effect. Einstein demonstrated that each particle of light, known as a photon or quanta, carries energy in the form of packets that vary in size depending on the frequency of the light being transmitted.

Photoelectric effect

In 1887, Hertz noticed that electrons are emitted from a metal surface when electromagnetic radiation falls on it. In 1888, Hallwachs showed experimentally that electrons are emitted from the Zinc plate when ultraviolet rays fall on the plate.

This phenomenon of emission of electrons from a metallic surface, when illuminated by the light of appropriate wavelength or frequency, is called the photoelectric effect. The electrons radiated in this process are called photoelectrons, and the current produced in the circuit is called photoelectric current.

In general, the photoelectric effect is a phenomenon exhibited by all substances when illuminated by radiation of a suitable wavelength.

Particle nature of light: The photon

Einstein gave his theory of the photoelectric equation which means that electrons do not absorb radiation continuously. Still, radiation energy is made up of discrete units called quanta of energy of radiation. He proved his theory and led to the following equation, commonly known as Einstein’s photoelectric equation. 

 KE = hv – hv0 

where KE is the kinetic energy of the photoelectron, h is Planck’s constant, v is the frequency of the photon, and v0 is the threshold frequency of material. The particle nature provides a valid reason for the behaviour of matter. It proves that particles of any matter are always moving; this explains solid, liquid and gas behaviour and properties.

• The photoelectric effect gave evidence that when light interacts with a matter, it behaves as a packet of energy that is hv. Each photon has its own energy E = hv and momentum p = hv/c, where c is the speed of light in a vacuum.
• Photons are not dependent on the intensity of the radiation used to strike the surface.
• Photos are not deflected by magnetic and electric fields, which are neutral.
• The total energy is conserved in photon-electron collisions.
• The particle nature is depicted in experiments such as the photoelectric and coupon effects. 

Einstein described the photoelectric effect by referring to light as having particles, as it does in nature.

Photoelectric work function

The photoelectric effect is the removal of the electron from an atom of a photosensitive material that is the most loosely linked. The surface material’s photoelectric work function (Ø0) is defined as the smallest amount of energy required to eject an electron from a specific surface when the surface material is a semiconductor. The work function of a metal surface is one of its distinguishing characteristics.

The work function can be expressed mathematically as

Ø0 = hv0

Conclusion

1. It is known as the photoelectric effect when light falls on a metal’s surface, causing electrons to emit from its surface due to the light falling on it.
2. The photoelectric effect is a phenomenon in which a metal surface emits electrons when touched by light with a specific frequency.
3. Einstein took advantage of Planck’s concept of light as a particle to address the previously occurred problem with the photoelectric effect.
4. The stopping potential, also known as the reverse potential, is the potential that is present when the photocurrent comes to a stop.
5. Regardless of the intensity of the light source, it will be able to pass through the stopping voltage.