Question

if the focal length of a convex lens is 20 cm and the focal length of a concave lens is 15 cm. If a lens is formed by combination of these two lenses find the power of new lens​

Answer 1

Answer:

f

1

=+10cm for convex lens

f

2

=−20cm for concave lens

The focal length of the combination is given by

f

1

=

f

2

1

+

f

2

1

f

1

=

+10cm

1

+

−20cm

1

=

20cm

1

f=+20cm

The correct option is B.