Definitions [4]
Define the work function of a metal. Give its unit.
The minimum energy needed for an electron to escape from the metal surface is called the work function of that metal. Its unit is electron volt (eV).
Definition: Electron Emission
The phenomenon of emission of electrons from the metal surface is called "Electron Emission".
Give the definition of intensity of light according to quantum concept and its unit.
Intensity of light refers to the strength or brightness or amount of light produced by a specific source. Its unit is the candela (cd).
Define stopping potential.
The minimum negative potential given to the anode of a photo-cell for which the photoelectric current becomes zero is called stopping potential.
Key Points
Key Points: Electron Emission
Three Types of Electron Emission:
| Type | Method | How |
|---|---|---|
| Thermionic Emission | Heat | Thermal energy is imparted to free electrons by heating. |
| Field Emission | Strong Electric Field (~10⁸ V/m) | Free electrons experience an electric force and are pulled out. |
| Photoelectric Emission | Electromagnetic Radiation | Light of suitable frequency falls on metal, electrons are emitted. |
| Secondary Emission | High-speed electrons/particles | Metal bombarded by fast particles; electrons are emitted. |
