Question

The size of the image formed by convex lens of focal lenght 20 cm is observed to be reduced 1/3rd of its size . Find the distance of object from the optical centre .

Answer 1

object distance is -80cm and image distance is -80/3 cm

Answer 2

Dear student,

● Answer -
u = -40 cm

● Explanation -
# Given -
h2/h1 = 1/3
f = 20 cm

# Solution -
Magnification by comvex lens is given by -
M = h2/h1 = -v/u
1/3 = -v/u
v = -u/3


According to lens formula -
1/f = 1/u + 1/v
1/20 = 1/u - 3/u
u = -40 cm

Therefore, object is 40 cm from optical centre of lens.

Hope this helped...