Define power of a lens and write its unit

Define power of lens and give its units.

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 lens and its and power used by each of the them ?

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 lens and power used by each of the them ?

Define power of a lens and give its ralation with focal length.