Question

A double convex lens of glass of refractive index 1.6 has its both surfaces of equal radii or curvature of 30 cm each. An object of height 5 cm is placed at a distance of 12.5 cm from the lens, calculate the size of the image formed.

Answer 1

Given :

μ=1.6

R1= +30cm

R2= -30cm

From lens makers formula :

1/f=(n-1)[1/R1-1/R2]

=(1.6-1)[1/30+1/30]

= 0.6x 2/30

=6x2/10x30

=1/25

f=25cm

u=- 12.5cm

ho=5cm

from lens formula :

1/f=1/v-1/u

1/v=1/f+1/u

=1/25 +1/12.5

=2+1/25

=3/25

v=25/3=8.33 cm

magnification =m= (hi/ho)= v/-u

 hi/5= 8.33/-12.5

hi =-3.33 cm

size of the image formed is -3.33cm