Question

Assertion: In He-Ne laser, population inversion takes place between energy levels of neon atoms. Reason: Helium atoms have a meta-stable energy level.

• A. If both assertion and reason are true and reason is the correct explanation of assertion
• B. If both assertion and reason are true but reason is not the correct explanation of assertion
• C. If assertion is true but reason is false
• D. If both assertion and reason are false

Answer 1

Answer: (B)

The transition in He-Ne laser is shown below.
An electric discharge in the gas pumps the helium atoms to higher energy states (which is metastable state $\approx {10}^{-8}\sec$ ) These He atoms collide with the ground state neon atoms and excite to higher states (levels) and produce an inverted population inversion causing a unidirectional photon beam (laser light).