Question

Define 1 dioptre power of a lens.

Answer 1

Hint – You need to know that a dioptre is a refractive power unit and is equal to the corresponding focal length of the lens. The strength of the lens is the capacity of the lens to concentrate the rays that fall on it.

Complete step by step answer:

Power ${\text{P = }}\dfrac{{\text{1}}}{{{\text{focal}}\,{\text{length(f)}}}}{\text{ = 1D}}$

Power of the lens is the ability of a lens to converge the rays falling on it.

One dioptre is the power of the lens whose focal length is 1m.

Note – To solve this problem you need to know that the power of the lens is reciprocal of its focal length. Here Power is denoted by P. SI unit of Power on the lens is Dioptre and it is denoted by D. You may note that the power of a convex lens is positive and that of a concave lens is negative.