Question

find position of an object which when placed in front of a convex lens of focal length 20 cm produces a virtual image which is twice size of object​

Answer 1

Given,

f = −20 and M = 2

We know that ;

=

=

We know,

M = -

Substituting the value of v ,

M = -

Substituting value of f = 20

M =

According to question,

M = 2

= 2

⇒20 = 2u + 40

⇒ u = − 10.

⇒

⇒  = 20

Hence,

The image is at distance of 20 cm from the mirror on the side opposite to that of object.