Question

Assertion : The radius of curvature of a mirror is double of the focal length.
Reason: A concave mirror of focal length $f$ in air is used in a medium of refractive index $2$. Then the focal length of mirror in medium becomes $2f$.

• 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: (C)

Focal length of a mirror does not depend on the medium in which mirror is held. It depends on the radius of the sphere from which it is made. However focal length of a lens does depend on medium.