A 5 cm tall object is placed perpendicular to the principal axis of a convex lens of focal length 20 cm. The distance of the object from the lens is 30 cm. Find the (i) positive (ii) nature and (iii) size of the image formed.
Given object size = 5 cm
u = -30 cm
f = 20 cm, v = ?
Using the lens formula 1/f = 1/v-1/u
We have 1/v = 1/u + 1/f = 1/-30 + 1/20 = -2+3/60 = 1/60
===> 1/v = 1/60
Therefore v = 60cm
Magnification v/u = 60/-30 = -2
Magnification = Image size/Object size
$h _{ i }$/$h _{ o }$ = -2
$h _{ i }$/5 = -2
$h _{ i }$ = -2x5 = -10 cm
The image is real inverted and magnified.