Question

Two lenses of power +1.5D &-0.5D are kept in contact with each other in contact on their principle axis. What is effective power of combination

Answer 1

ower of the combination = P1 +P2

P = 3.5 - 1.5 = 2 D.

P =1/f

f = 1/P = 1/2 = 0.5 m.

u = 0.8 m.

Apply lens formula

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

1/v = 1/f - 1/u

V = uf/u - f

v = 0.8 × 0.5/0.8-0.5

Hence v = 1.33 m.

Image formed at a distance of 1.33 m from the lens

Hope this helps...