| English | Thermionic emission |
|---|---|
| Bahasa Melayu | Pancaran termion |
| 中文 | 热电子发射 |
Definition
The release of electrons from the surface of a heated metal when it is given enough thermal energy.
In exam terms
Thermionic emission is the release of electrons from the surface of a heated metal when it is given enough thermal energy to overcome the forces holding the electrons in. The hotter the metal, the more electrons are emitted per second.
There is no single SI unit for the process itself; it is described qualitatively in terms of temperature and rate of emission.
Example of correct use: in a cathode-ray tube, the cathode is heated by a filament so that thermionic emission produces a supply of free electrons that can then be accelerated.
Do not confuse it with…
Do not confuse thermionic emission with the photoelectric effect. In thermionic emission electrons are freed by heat (thermal energy); in the photoelectric effect they are freed by light (photon energy).
Both release electrons from a metal but the energy source differs.
In Paper 2 you may be asked to define thermionic emission or to explain why increasing the filament current increases the electron supply; link the higher temperature to more electrons gaining enough energy to escape.
Source: DSKP KSSM Physics Form 4 and 5 (Versi English) (Bahagian Pembangunan Kurikulum (BPK), KPM)