Question

A tripled size virtual image of an object place at a distance of a20cm from the lens is formed by the lens. Find the distance of the image form the lens and focal length of the lens

Answer 1

Answer:

Correct option is

C

concave and f=40 cm-

u=−20

m=

u

v

=

3

2

⇒v=

3

2

u=

3

2

×(−20)=

3

−40

v

1

−

u

1

=

f

1

⇒

40

−3

+

20

1

=

f

1

⇒f=−40cm

∴ lens is concave with focal length 40cm.

Hence,

option (C) is correct answer.