Two equi-convex lenses of focal lengths 20 cm and 30 cm respectively are placed at a separation 'd' with their principal axes coinciding. An object placed at a distance 'u' from the first lens, forms an image at a distance v from the second lens. Find the ratio `(u)/(v),` if it is observed that u and v have the same set of values for d = 30 cm, 60 cm, 120 cm and 150 cm.

Options

A. `1/2`
B. `2/3`
C. 2
D. `3/2`

Answer

D

Explanation

The object and image positions relative to their closest lenses do not depend on the separation between the two lenses. So the rays between the lenses are parallel. Object is at the focus of the first lens and image at the appropriate focus of the second lens.
`implies (v)/(u)= (f _(2))/(f _(1)) = (30)/(20) = (3)/(2)`