Differentiate between CONVEX LENS and CONCAVE LENS.

Convex lenses are thicker in the middle than at the edges. They refract toward the center. Only people have convex lenses. Concave lenses are used in telescopes and glasses. Concave lenses are thinner in the middle than at the edges. When light passes through concave lenses always bend away from each other toward the edges of the lens.
A convex or "positive" lens is thicker in the middle and thinner at the edges. A concave, or "negative" lens is thinner at the middle and thicker at the edges. Convex lenses project a real image behind the lens; concave lenses project a virtual image in front of the lens.