A diverging lens with magnitude of focal length `25 cm` is placed at a distance of `15 cm` from a converging lens of magnitude of focal length `20 cm`. A beam of parallel light falls on the diverging lens. The final image formed is.

Options

A. Real and at a distance of 40 cm from convergent lens
B. Virtual and at a distance of 40 cm from convergent lens
C. Real and at a distance of 40 cm from the divergent lens
D. Real and at a distance of 66 cm from the convergent lens

Answer

A

Explanation

As the parallel beam is incident on the concave ( diverging) lens, a virtual image will appear at its focus. Thus, the image distance `v = -25` cm
This image formed by the concave ( diverging) lens will behave as object for the convex ( converging) lens.
Thus, the object distance for the convex lens
`u = -25 - 15 = -40 cm`
Focal length, `f=20` cm
Let `v` be the distance of the final image from the convex lens.
Applying lens formula :
`1/v - (1)/ ((-40))= (1)/(20)`
`v = 40` cm
Thus, the final image is formed at a distance of 40 cm from converging lens and it is real and inverted.