Answer:
Tungsten is used as an electron emitter as it has a very high melting point (3655 K) and moderate work function.
- Tungsten is a suitable metal for Thermionic emission, has a high melting point of 3655 K, but its work function is high at about 4.52 eV. It starts emission at 2500 K.
- If thoriated tungsten (coated with carbon and thorium) is used work function reduces to 2.6 eV and emission begins at 2000 K.
- If tungsten is coated with barium and strontium oxide work function reduces to 1 eV and emission begins at 1000 K and a good supply of electrons is obtained.
