Question

A concave lens forms a virtual image 0.8 times the size of the object. The distance between object and image is 5.3 cm: Find the focal length of the lens. Write your answer in units of cm. ​

Answer 1

Answer:

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.