Power of lens Is the degree of convergence and divergence provided by a lens and its unit is Diopter (D).

The focal length of the lens used by the first student is in positive so it is a convex lens. The lens used by the second student is a concave lens.

p=1/f

p=1/0.5

p=2

The power of lens used by 1^st student =+2

The power of lens used by 2^nd student = -2