Question

A divergent lens of focal length 30 cm forms the image of an object of size 6 cm on the same side as the object at a distance of 15 cm from its optical centre. Use lens formula to determine the distance of the object from the lens and the size of the image formed.

Answer 1

Given:

f = −30 cm 

h₀ = 6 cm

v = −15 cm 

Using the lens formula,

`1/f  = 1/v - 1/u`

⇒ `1/u = 1/v - 1/f`

⇒ `1/(-15) - 1/(-30)`

= `-1/30`

∴ u = −30 cm

Using the formula,

`m = h_i/h_0 = v/u`

We get,

`h_i = v/u xx h_0`

= `(-15)/(-30) xx 6`

= 3 cm

∴ A diminished image is formed and its size is 3 cm.