A concave lens has focal length of 15 cm. At what distance should an object from the lens be placed so that it forms an image at 10 cm from the lens ? Also, find the magnification of the lens.

Options

A. `-30 cm`
B. `+30 cm`
C. `-60 cm`
D. `-45 cm`

Answer

A

Explanation

Here, focal length of lens, `f = -15 cm`,
image distance, `v = -10 cm`, object distance, `u = ?`
From `(1)/(f) = (1)/(v) - 1/u`
`1/u = (1)/(v) - (1)/(f) = 1/(-10) + 1/15 = (-3 +2)/(30) = (-1)/30`
or `u = - 30 cm`.
The ray diagram of image formation is shown in Fig.