Question

The emission of a photon without the use of an external agency for its emission in a system is known as __________.
A. light amplification
B. induced absorption
C. stimulated emission
D. spontaneous emission

Answer 1

The emission of photons without the help of any external things is referred to as the spontaneous emission. It is a phenomenon in which a system which is in an excited energy state will get transited to a lower energy state by emitting photons of a specific energy. This will help you in solving this question.

Complete answer:
The phenomena are referred to as induced absorption and induced emission, respectively. A molecule in an excited high energy state can release electromagnetic radiation while coming back to some lower energy level in the presence of induced radiation. This is known as induced absorption. The transition of an electron from the excited higher energy state to the ground state can occur because of the natural tendency of the electron without the action of any external agent. The radiation created because of such transitions are referred to as spontaneous radiation.

So, the correct answer is “Option D”.

Note:
Suppose an electron is in an excited state in a semiconductor substance which is illuminated by an external photon, the externally incident photons may result in the electron in the excited state to come down to the ground state by the release of the excess energy as a photon. In this process, the externally incident photon does not get absorbed in the process. It starts the production of this new photon by making the electron in the excited state to release its energy and come down to the ground state. Stimulated emission is the phenomenon with which the photons are helpful in producing other photons which are having the similar phase and wavelength as that of the parent photon.