The lens of power + 1.0 D is:

1. convex of focal length 1.0 cm
2. convex of focal length 1.0 m
3. concave of focal length 1.0 cm
4. concave of focal length 1.0 m.

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 - ?