Question

Determine how far an object must be placed in front of a converging lens of focal length 10 cm in order to produce an erect (upright) image of linear magnification 4.

Answer 1

Given:

Focal length, f = 10 cm

Magnification, m = +4 (Image is erect.)

Object distance, u = ?

Applying the magnification formula, we get:

m = `v/u`

4 = `v/u`

v = 4u

Applying the lens formula, we get:

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

`1/(4u)- 1/u = 1/10`

u = `-30/4`

u = −7.5 cm

Thus, the object must be placed at a distance of 7.5 cm in front of the lens.