Question

Q5: A converging lens of focal length 15.0 cm forms images of an object situated at various distances. (a) If the object is placed 20.0 cm from the lens, locate the image, state whether it's real or virtual, and find its magnification. (b) Repeat the problem when the object is at 15.0 cm and (c) again when the object is 10.00 cm from the lens.

Answer 1

a) for converging lens

focal length is f = 15 cm

do = 20 cm

the using

1/f = (1/do)+(1/di)

1/15 = (1/20)+(1/di)

di = 60 cm

real image behind the lens at a distance 60 cm

magnification is m = di/do = 60/20 = 3

b) d0 = 15 cm

1/f = (1/do)+(1/di)

1/15 = (1/15)+(1/di)

di = infinite ,no image forms

magnification is m = infinite

c) do = 10 cm

1/f = (1/do)+(1/di)

1/15 = (1/10)+(1/di)

di = -30 cm

image forms at the same side of the object at a distance 30 cm from the lens

virtual image

magnification is m = di/do = 30/10 = 3