A convex lens has a focal length 15 cm. A student obtains a clear sharp image of an object by placing it at 20 cm distance from the lens. At what distance approximately will he obtain an image of magnification - l ?

Explanation

Convex lens `f=+15 cm, u = -20 cm , m = -1`
Magnification (m) `=(v)/(u)`
`-1=((v))/((-20))rArr v=+20 cm`
An image of magnification - 1 will be obtained at 20 cm