A real image of an object is formed at a distance of `20 cm` from a lens. On putting another lens in contact with it, the image is shifted `10 cm` towards the combination, Determine the power of the second lens.

Options

A. 2D
B. 5D
C. 6D
D. 10 D

Answer

B

Explanation

As image formed is real, therefore lens must be convex, `v` = 20 cm. Let `f_(1)` , be focal length for this lens.
`therefore(1)/(10)-(1)/(u)=(1)/(f_(1))+(1)/(f_(2))=((1)/(20)-(1)/(u))+(1)/(f_(2))rArrf_(2)= 20` cm
`thereforeP=(100)/(20)m^(-1)=5D`