Question

a convex lens of focal length 20 cm is combined with another lens so that the power of combination is -5D find the focal length of another lens

Answer 1

Power of convex lens = 100/20 = 5 D

For combination of lenses

P = P₁ + P₂

-5 = 5 + P₂

P₂ = -10D

f₂ = -100/10 = -10 cm

Answer 2

-10 is the answer of the question