question_answer

Direction for: In each of the following questions a statement of Assertion is given followed by a corresponding statement of Reason just below it. Of the statements mark the correct answer as

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

Correct Answer: B

Solution :

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).