Question

Find the power of lens whose magnification is -1 and object distance is 20cm

Answer 1

Answer:

10D

Explanation:

m=v/u

-1=v/-20

v=-20*-1

=20 cm

it is a convex lens

1/f=1/v - 1/u

= 1/20 - 1/-20

1/20+1/20

=2/20

f=20/2=10cm

now

P=1/f

=1/10

=100/10

=+10D