Question

A concave lens of focal length is 20 cm and convex lens is 25 cm what will be its power in dioptre seperao​

Answer 1

Answer:

The net focal length of the combination is

f

1

=

f

1

1

+

f

2

1

=

+25

1

+

−20

1

=−

100

1

⟹f=−100cm

Power of combination=P=P

1

+P

2

=

f

1

1

+

f

2

1

P=

0.25

1

+

−0.20

1

=

25

100

−

20

100

=

100

400−500

=−

100

100

=−1

⟹P=−1D

Since power is negative, the combination is diverging.