Question

Find the power of a convex lens which forms a real and inverted image of magnification -1 of an object placed at a distance 20cm from its optical centre

Answer 1

Answer:

The Power is 10D

Explanation:

v/u=m

given m = -1

therefore

v/u=-1

v=  -u

i/v - 1/u = 1/f

from above derived equation

-1/u -1/u = 1/f

-2/u = 1/f

given  u = -20 cm

on substituting it in above equation we get

-2/-20 = 1/f

on solving this we get

f =10

power of lens = 100/f(in cm)

                       = 100/10

                       =10 D

therefore the power of the above lens is +10D