Electron Emission
According to the modem atomic theory, the atom is composed of the three fundamental particles, which are invisible to bare eyes. These are:
- Neutron
- Proton
- Electron
The electrons are fully stretched towards the nucleus due to the nuclear pull termed as the “work function”. Whenever the electrons are to be evolved from the surface, we have to apply a force in opposite direction in the form of some external energy greater than the work function.
The emission of electrons from the metallic surface with the use of some external energy is termed as “electron emission”.
Atomic structure
Types of Electron Emission
Electron emissions are categorized with respect to the energy used for the emission of electrons from the surface of the metal. According to this formula, types of electron emission are briefed below:
1. Primary Emission
Primary emission is such a type of electron emission in which heat is used as the external source of energy for the removal of electrons from the metallic surface. It is also termed as thermionic emission. The factor on which thermionic emission depends is the amount of heat used, the more the input heat more the thermionic emission.
Thermionic Emission
2. Secondary Emission
Secondary emission is such of electron emission in which primary electrons ( emitted in thermionic emission) are employed for the emission of secondary electrons from the metallic surface. Factors on which secondary emission depends upon are:
- No. of primary electrons
- Mass of primary electrons
- The intensity of primary electrons
- Speed of primary electrons
- Type of metallic surface
Secondary emissions are directly proportional to mass, intensity, speed, and no. of primary electrons. The more these factors are, the more will be the secondary emission.
Secondary Emission
3. Photo Emission
Photoemission is such a type of electron emission in which light energy is used as the external source of energy for the removal of electrons from the metallic surface. Factors on which photoemission depends upon are:
- Frequency of light
- Speed of light
- Intensity of light
Photoemission is directly proportional to the frequency, speed, and intensity of light. The more these factors are, the more will be the photoemission.
Photo Emission
4. Field Emission
Field emission is such a type of electron emission in which strong positive field energy is used as the external source of energy for the removal of electrons from the metallic surface. Factor on which field emission depends upon is the strength of the positive field. The more the strength of the positive field, the more is the emission of electrons from the metallic surface.