Question

An object of height 4 cm is placed at a distance of 20 cm from a concave lens of focal length 10 cm. Use lens formula to determine the position of the image formed.

Answer 1

Object distance, u = 20 cm

Image distance, v = ?

Focal length, f = 10 cm

As per the sign conventions used,

f = −10 cm

u = −20 cm

According to the lens formula,

`1/f=1/v-1/u`

`1/v=1/f+1/u`

`1/v=1/-10+1/-20=-3/20`

`rArrv=-20/3=-6.6" cm"`

The image is formed at a distance of 6.6 cm from the lens at the same side where the object is placed.