Question

A convex lens form a real image four times magnified at a distance of 60 cm from the lens .Calculate the focal length and power of lens.

Answer 1

given :

magnification=m=-4[since it is real and magnified]

v= 60cm

object distance=u=?

magnification =m=V/u

u= 60/-4 =-15cm

Focal length=f=?

f=1/v - 1/u

=1/60 +1/15

=4+1/60

=5/60

f=60/5

=12cms

∴ Foal length of convex lens=12cm

Power=P=?

p=1/f (in m)

=100/f ( in cm)

=100/12

=+8.33 Diopters

∴ P=+8.3 D