Define one dioptre of power of a lens.

a) What do you understand by the power of a lens? Name one factor on which the power of a lens depends. b) What is the unit of power of a lens? Define the unit of power of a lens. c) A combination of lenses for a camera two converging lenses of focal length 20 cm and 40 cm and a diverging lens of focal length 50 cm. Find the power and focal length of the combination.

One dioptre is the power of a lens of facal length

What is the power of a lens ?