At what distance an object must be placed from a lens of focal length 15 cm to get an inverted image of unit magnification ?

Options

A. 15 cm
B. 20 cm
C. 25 cm
D. 30 cm

Answer

D

Explanation

The lens must be a convex lens, as it is giving an inverted image of unit magnification. For a concave lens, the image is virtual and erect and `m lt1`.
Since the image is inverted, it must be a real image and since the magnification is unity.
`therefore (I)/(O) =1=(v)/(u) therefore v=u`
(Virtual images are always erect. )
In the case of a convex lens, this is possible if the object is placed at a distance 2f from the lens.
i.e. If `u=2f, v=2f therefore u=2f =2xx15 =30 cm`