question_answer

The refractive index of the material of a concave lens is m. It is immersed in a medium of refractive index \[{{\mu }_{1}}.\] A parallel beam of light is incident on the lens. The path of the emergent rays when \[{{\mu }_{1}}>\mu \] is:         [JEE ONLINE 12-04-2014]

A)

B)

C)

D)

Correct Answer: A

Solution :

[a] If a lens of refractive index m is immersed in a medium of refractive index m1, then its focal length in medium is given by

If  is the focal length of lens in air, then

If then and  have opposite signs and the nature of lens changes i.e. a convex lens diverges the light rays and concave lens converges the light rays. Thus given option [a] is correct.