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 convex lens and the image at a distance of 26 cm from the convex lens, calculate the new size of the image

Options

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

Answer

B

Explanation

Convex lens will form image `I_(1)` at its focus which acts like a virtual object for concave lens.
Hence for concave lens `u=+4 cm, f=20 cm`. So by lens formula `(1)/(-20)=(1)/(v)-(1)/(4)impliesv=5 cm ` i.e. distance of final image `(I_(1))` from concave lens `v=5cm` by using `(v)/(u)=(I)/(O)implies(5)/(4)implies(I_(2))=2.5cm`