A lens of focal length 20 cm forms an inverted image at a distance 60 cm

Light (10)

A lens of focal length 20 cm forms an inverted image at a distance 60 cm from the lens.

1. Identify the lens.
2. How far is the lens present in front of the object?
3. Calculate the magnification of the image.

Answer

(i) Convex lens

(ii) f = 20 cm, v = 60 cm

1/f = 1/v = 1/u

1/20 = 1/60 - 1/u

1/u = 1/60 - 1/20

1/u = -1/30

u = - 30 cm

(iii) m = v/u

= 60/-30

= -2