A converging beam of rays in incident on a diverging lens. Having passed through the lens the rays intersect at a point `15 cm` from the lens. If the lens is removed, the point where the rays meet, move `5 cm` closer to the mounting that holds the lens. Find the focal length of the lens.

Options

A. `-30` cm
B. 5 cm
C. `-10 ` cm
D. 20 cm

Answer

A

Explanation

`(1)/(v) - (1)/(u) - (1)/(f)`
`rArr " " (1)/(f) = (1)/(15) - (1)/(10)`
`rArr " " f= - 30` cm.