Question

An object is placed at a distance of 4 cm from a concave lens of focal length 12 cm. Find the position of the image.

Answer 1

Given,

Object distance, u = -4 cm

Focal length, f = -12 cm

From the lens formula

We know,

$\frac{1}{f}$ = $\frac{1}{v}$ - $\frac{1}{u}$

Or we can write

$\frac{1}{v}$ = $\frac{1}{f}$ +$\frac{1}{u}$

$\frac{1}{v}$ = $\frac{-1}{4}$ - $\frac{1}{12}$

$\frac{1}{v}$ = -$\frac{1}{3}$

Thus, the image distance will be, v = -3 cm

Image will form in same side as the object at the distance of 3 cm from the lens.