A concave lens of power - 2D is placed in contact with a convex lens of power + 1.5D what will be the resultant power

Answer: - 0.5 D

Explanation:

The resultant power can be defined as the sum of powers of all the lenses placed in contact together.

P = P₁ + P₂ + P₃ + ...

It is given that power of the concave lens is, P₁ = - 2 D

Power of the convex lens is, P₂ = + 1.5 D

Thus, the resultant power when these two lenses are placed in contact with each other are: P = P₁ + P₂ = - 2 D + 1.5 D = - 0.5 D.