Question

find the power of the convex lens which forms a real image of magnification -1 of an object placed at a distance of 20 cm

Answer 1

m=-1

u=-20

to find v

m=-v/u = -1

v=-20

to find focal length

1/f = 1/v -1/u = 1/10

f = 1m

p=1/f

p= 10 dioptre