What is the power of lens?

Answer the following questions : What is the power of a lens ?

Solve the following examples/ numerical problems: A spherical lens is used to obtain an image on a screen . The size of the image is four times the size of the object. What is the type of lens and at what distance is the screen placed from the lens ?

What is power of a lens?

If for a lens , f= -20 cm, what is the power of the lens ?

What is the power plant shown in diagram based on?

Three lenses having power 2, 2.5 and 1.7 D are kept touching in a row. What is the total power of the lens combination?

For a particular glass lens f = - 2 m. Only this much data was provided to a student. He was told to calculate the power of lens and to find out type of lens given to him. His answer must be _____