Question

At what distance should an object be placed from a convex lens of focal length 18 cm to obtain an image at 24 cm from it on the other side? What will be the magnification produced in this case?

Answer 1

Given:

Focal length, f = 18 cm

Image distance, v = 24 cm

Putting these values in the lens formula, we get:

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

`1/24 - 1/u = 1/18`

`-1/u = 1/18 - 1/24`

`-1/u = (4 - 3)/72`

`-1/u = 1/72`

u = −72 cm

The object should be placed at a distance of 72 cm from the convex lens.

Magnification, m = `v /u`

= `24/ (-72)`

= `-1/3`