Question

The magnification of an image formed by a lens is – 1. If the distance of
the image from the optical centre of the lens is 35 cm, where is the object
placed? What is the nature and focal length of the lens? If the object is
displaced 20 cm towards the optical centre of the lens, where would the image
be formed and what will be its nature? Draw a ray diagram to justify your
answer.

Answer 1

Answer:

object is placed at 35cm on the side opposite to that where image is placed

f=35/2cm

Explanation:

given,

m= -1

v=35cm

m=v/u(for lens)

-1 =35cm/u

u= -35cm

1/f=1/v - 1/u

1/f=1/35-(1/-35)

1/f=2/35

f=35/2cm

u=-20cm

$\frac{1}{35/2} = \frac{1}{v} - \frac{1}{-20}$

$\frac{2}{35} - \frac{1}{20} = \frac{1}{v}$

$\frac{1}{v} = \frac{1}{140}$

v=140cm