Question

A concave lens of focal length = 30cm if an object of size 4cm is placed 20cm from the lens find Nature, size and magnification of image.

Answer 1

given, focal length of concave lens, f = -30cm

size of object = 4cm

object distance from the lens, u = -20cm

using lens maker formula,

1/v - 1/u = 1/f

or, 1/v - 1/-20 = 1/-30

or, 1/v = -1/20 - 1/30

or, 1/v = -5/60

or, v = -12 cm

magnification, m = v/u

size of image/size of object = (-12/-20)

or, size of image/4cm = 3/5

or, size of image = 2.4 cm

here it is clear that size of image is smaller than size of object.

Nature : virtual and diminished

Size : 2.4cm

magnification: 0.6