An object is placed at a distance of `1.5 m` from a screen and a convex lens is interposed between them. The magnification produced is `4`. What is the focal length of the lens ?

Answer

`0.24 m`

Explanation

Here, `|u| + |v| = 1.5` …(i)
`m = -4 = (v)/(u) :. u = -(v)/(4)`
From (i), `(v)/(4) + v = 1.5 v = 1.2m` ,
`u = - (1.2)/(4) = - 0.3m`
`f = (u v)/(u - v) = (-0.3 xx 1.2)/(-0.3 - 1.2) = 0.24 m`