The focal length of a thin convex-lens is 30cm. At a distance of 10 cm from the lens there is a plane refracting surface of refractive index `3//2` Where will parallel rays incident on lens converge?

Options

A. At a distance of `27.5 cm` from the lens
B. At a distance of `25 cm` from the lens
C. At a distance of `45 cm` from the lens
D. At a distance of `40cm` from the lens

Answer

D

Explanation

The lens will converge the rays at its focus `i.e., 30cm` from the lens or `20 cm` from the refracting surface.
`PI_(1)=20cm`
`:. PI_(2)=m(PI_(2))`
`=(3)/(2)xx20=30cm`
So, the rays will converge at a distance of `40cm` from the lens.