Concave Mirror: It is a spherical mirror whose outer surface is polished and inner or concave side is reflecting surface. Convex Mirror: It is a spherical mirror whose inner surface is polished and whose outer side or convex side is the reflecting surface. f = \(\frac{m}{4}\) = f = \(\frac{d}{4}\) f = \(\frac{20}{4}\) = 5cm (For metal, it is the polished side that will be the reflecting surface)