An object of height 2 cm is placed in front of a convex lens of focal length 20 cm at a distance of 15 cm from it. Find the position and magnification of the image.

Explanation

Given, 0 = 2 em (positive), f = 20 cm (positive), u = 15 cm (negative)
From lens formula `1/v-1/u=1/f,1/v-1/((-15))=1/(20)`
or `1/v=1/(20)-1/(15)=(-1)/(60)` or v = 60 cm (negative)
Thus image is formed in front of lens at a distance 60 cm.
Magnification `m=v/u=(-60cm)/(-15cm)`
i.e. Image is erect in size (=8cm) four times the object