Question

the image is formed by a diverging lense of focal length f .the size of image is one fourth to that of real image find the distance of object from the lenses.​

Answer 1

Explanation:

Concave lens forms the virtual image of a real object. So, let

u=−4x and v=−x

Then, 3x=10 cm

or x=

3

10

cm

∴u=−

3

40

cm and v=−

3

10

cm

Substituting in

f

1

=

10

−3

+

40

3

or f=−

9

40

or f=−4.4 cm.

Answer 2

Given:

Diverging lens

Focal length f

Image size = 1/4 th of the size of the object

To find:

Find the distance of the object from the lens.​

Solution:

m = 1/4

m = v/u

v/u = 1/4

v = u/4

1/f = 1/v + 1/u

1/f = 4/u + 1/u

1/f = 5/u

f = u/5

u = 5f