The image obtained with a convex lens is erect and its length is `4` times the length of the object. If the focal length of lens is `20 cm`, calculate the object and image distances.

Options

A. - 15 cm, - 60 cm
B. 45 cm . - 60 cm
C. 12 cm, 20 cm
D. None

Answer

A

Explanation

Here, ` m = v/u = 4 or v = 4 u, f = 20 cm, u = ? v = ?`
As `(1)/(v) -1/u = (1)/(f), 1/(4u) - 1/u = 1/20`
or `(1 - 4)/(4u) = 1/20 , 4u = -60 or u = -15 cm`
and `v = 4u = 4(-15) = -60 cm`.