Define the principal focus of the concave mirror. Write two uses of convex mirrors.

Hint: Focus means where the light focuses. Light gets converged when it reflects from the surface of a concave mirror whereas it gets diverged when it is reflected from the surface of a convex mirror.

Complete answer step by step:
Principle focus:
When light rays parallel to the principal axis coming from infinity fall on the surface of the concave mirror, it converges at a single point on the principal axis. This point is called ‘Principal Focus of concave mirrors. The principal focus is also referred to as simply focus or focal point. The concave mirror focal point lies in front of the mirror.

As shown in above figure, parallel rays coming from infinity converge at principal focus F.
Uses of convex mirror:
1. Convex mirrors are used as side mirror in vehicles as they provide wider field of view
2. To eliminate blind spots they are hanged or mounted at the corners of hallways or roads.
3. As convex mirrors diverge the light, it is used in street light for more spread of light.
Additional Information:
The concave and convex mirrors are two types of curved mirrors. Concave mirrors are used where we want to converge light and convex mirrors are used where we want to diverge the light. The principal focus of convex mirrors lies behind the mirror therefore light appears to be diverging when it gets reflected from the convex mirror.

Note: Do not get confused between these two types of mirrors. Many times students get confused between convex and concave mirrors especially about their shapes. Simple way to remember their shapes is to remember their applications. It is easy to visualize their shapes once you understood their principle of working.