Question

Assertion : The mirror used in search lights are parabolic and not concave spherical. 

Reason : In concave spherical mirror the image formed is always virtual.

Mark the correct choice as

(a) If both assertion and reason are true and reason is the correct explanation of the assertion.

(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.

(c) Assertion is true, but reason is false.

(d) Assertion is false, but reason is true.

Answer 1

(c) The assertion is true, but the reason is false

Correct explanation:

In search lights, we need an intense parallel beam of light. if a source is placed at a focus of a concave spherical mirror only paraxial rays are rendered parallel. Due to large aperture of mirror, marginal parallel. Due to large aperture of mirror, marginal rays give a divergent beam. But in case of parabolic mirror, when source is at the focus, beam of light produced over the entire cross – section of the mirror is a parallel beam