Question

A small object is so placed in front of a convex lens of 5 cm focal length that a virtual image is formed at a distance of 25 cm. Find the magnification.

Answer 1

Given:
Focal length, f = 5 cm
Image distance, v =-25 cm (Image is virtual.)
Applying the lens formula, we get:
1/v  -1/u = 1/f (u = Object distance)
1/(-25)  -1/u = 1/5
or, 1/u =1/(-25)-1/5
or, 1/u =-6/25
or,
u = -25/6 cm
Now,
Magnification, m = v/u
                            = (-25)/(-25/6)
                            = +6