question_answer 68)

  Define power of a lens. What is its unit? One student uses a lens of focal length 50 cm and another of -50 cm. What is the nature of the length and its power used by each of them?

Answer:

                  Power of lens is defined as the ability of a lens to bend the rays of light. It is given by the reciprocal of focal length in metre. Its unit is dioptre. If focal length, (f) = 50cm, then, lens is convex. If focal length,   (f) = - 50 cm, then, lens is concave.