Question

How is light emitted?

(a) Klystron valves

(b) Radioactive decay of the nucleus

(c) Transmission of high energy electrons from an excited state to a lower state

(d) Acceleration of electrons

I had been asked this question during an online interview.

Origin of the question is Light in section Optics of Engineering Physics II

Answer 1

Correct option is (c) Transmission of high energy electrons from an excited state to a lower state

Easy explanation: An electron is always stable in the ground state. When in an excited state, it tends to jump to a lower state. In this process, it releases a photon of energy equal to the energy difference. When the frequency of these photons lies in the visible region, we get light.