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 of 20cm from it's optical centre

Answer 1

Answer:

m= -1

u= -20cm

m=v/u

-1=v/-20

20=v

v=20cm

1/v-1/u=1/f

1/20-1/-20=p

0.1 D=p

Answer 2

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

HOPE IT HELPS UH ✌