A concave lens forms an erect image of 1/3rd the size of the object which is placed at a distance 30 cm in front of the lens. Find:

(a) The position of the image, and

(b) The focal length of the lens.

The power of a lens is -2.0 D. Find its focal length and its kind.

The power of a lens is +2.0 D. Find its focal length and state what kind of lens it is?

The focal length of a convex lens is 25 cm. Express its power with sign.