Question

A lens forms a virtual, erect and diminished image of an object placed at a distance of
2m from it. The size of the image formed is half of that of the object. Which of the following statement is correct regarding the nature and focal length of the lens?

Answer 1

given

Image is virtual , so v<0

Magnification is

u

v

=0.5

v=0.5u

u=−2 ; v=−1

v

1

−

u

1

=

f

1

1

−1

+

2

1

=

f

1

f=−2m

concave lens as f<0

Answer 2

Explanation:

1/f=1/v -1/u

1/f=1/2-1/1/2

1/f=1/2-2/1

1/f=2-4/2

1/f=2/2

1/f=1/1

f=-1