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 fo refractive inidex `3//2` Where will parallel rays incident on lens converge?

Explanation

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