When light of suitable frequency falls on a metal surface and causes the ejection of electrons, the process is called
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → photoelectric emission
An electron can leave a metal only if it is given at least the work function. The processes of electron emission differ in how this energy is supplied.
Option (1) thermionic emission — Incorrect. In thermionic emission the energy comes from heating the metal. Light plays no part in it.
Option (2) photoelectric emission — Correct. Here the energy is supplied by light of suitable frequency, and the emitted electrons are called photoelectrons.
Option (3) field emission — Incorrect. In field emission a very strong electric field (of the order of \( 10^{8}\,\mathrm{V\,m^{-1}} \)) pulls the electrons out, as in a spark plug.
NCERT (2026-27):
Electron Emission – “(iii) Photoelectric emission: When light of suitable frequency illuminates a metal surface, electrons are emitted from the metal surface. These photo(light)-generated electrons are called photoelectrons.”