The focal length of a lens is (i) positive, (ii) negative. In each case, state the kind of lens.

What information about the nature of the image (i) real or virtual, (ii) erect or inverted, do you get from the sign of magnification + or - ?

How does the power of a lens change if its focal length is doubled?

How is the sign (+ or -) of power of a lens related to its divergent or convergent action?