- Degree of convergence and divergence provided by a lens is called power of the lens.
- Unit of power of lens is Diopter D.
- Focal length of lens used by first student is in positive hence it is a convex lens.
- The lens of second student is a concave lens.

**p = 1/f**

= 1/0.5

= **2**

Power of lens (first student) =+2

Power of lens (second student) = -2