Photons are the packets of energy which makes up the light, according to Einstein. Photons do not have a mass of their own but they do have energy and momentum.
There is a certain amount of energy which is required to eject an electron from its metal surface. Work function, or the needed energy, depends on the metal. Electrons gain energy by coming in contact with the photons. If the work function is as big as the energy of a photon, the energy can then be transferred to the electron, making the electron strong enough to escape from the metal surface.
Thus, the photoelectric effect is the process through which the electromagnetic radiation ejects the electrons from the material. Einstein was the one who proposed the fact that photons are the quanta of electromagnetic radiation with energy.
Photoelectric effect was discovered and given by Heinrich Rudolf Hertz (German physicist) in 1887. He was working on radio waves when he noticed that when an ultraviolet light shines on metal electrodes having applied voltage, then the light changes the voltage, causing a sparking. This concept of light and electricity was later taken up by Philipp Lenard in 1902.
Photoelectric effect is based on the concept that photons are a series of particles that make up an electromagnetic radiation. Electrons get emitted when a photon hits an electron on the metal surface. The resulting emitted electrons are known as photoelectrons.
INTERNAL AND EXTERNAL PHOTOEMISSION
When photoelectron is not emitted in a vacuum, but is emitted into a solid, then it is known as internal photoemission.
When photoelectron is emitted into a vacuum, then it is known as external photoemission.
The photons of a light beam have their characteristic energy which is proportional to the frequency of light. In the process of photoemission, if the electron acquires more energy than the work function of the material, then it gets ejected. However, if the photon energy is low, the electron cannot escape the material. The energy of the electrons that are emitted, do not depend on the incoming light’s intensity. But it does depend on the energy of the individual photons. The remaining of the energy, leftover from the energy used to free the electron, contributes to the electrons kinetic energy as a free particle.
- Photodiodes contribute to the field of image technology.
- Image intensifiers, light amplifiers, television camera tubes- all work on the principle that electron emission from cathode is determined by the amount of photons arriving that point.
- Photomultipliers are used whenever the low levels of light need to be detected.
- Gold leaf electroscopes are made in such a way that they are able to detect static electricity.
- Photo static copying.
- All the night vision devices.