The size of the image of an object, which is at infinity, as formed by a convex lens of focal length 30 cm is 2 cm. If a concave lens of focal length 20 cm is placed between the convax lens and the image at a distance of 26 cm from the convex lens, calculate the new size of the image.

Options

A. 1.25 CM
B. 2.5 cm
C. 1.05 cm
D. 2 cm

Answer

B

Explanation

Image formed by convex lens at `I_(1)` will act as a virtual object for concave lens . For concave lens

`(1)/(v) - (1)/(u) = (1)/(f) implies (1)/(v) - (1)/(4) = (1)/(-20) implies v = 5 cm`
Magnification for concave lens m `= (v)/(u) = (5)/(4) = 1.25`
As size of the image at `I_(1)` is 2 cm . Therefore , size of image at `I_(2)` will be `2 xx 1.25 = 2.5` cm.