A spherical mirror in which reflecting surface is towards the centre of the sphere of which the mirror is a part, is called concave mirror, i.e., reflection of light for this mirror occurs at concave surface or bent-in surface.
The rays of light incident on concave mirror in a direction parallel to the principal axis, actually meet at a single point F on the principal axis of the mirror. This point is called principal focus of the mirror.
Read the above passage and answer the following questions :
(i) Is principal focus of a concave mirror, a real point or a virtual point?
(ii) What happens in case of a convex mirror ?
(iii) Our teachers and parents advise us to stay focussed. What does it imply?

Explanation

(i) The principal focus F of a concave mirror is a real point. This is because the rays of light,on reflection from the mirror meet actually at F.
(ii) In case of a convex mirror, reflection of light occurs at convex surface or the bulged out surface. Principal focus F, in this case is a virtual point, as reflected rays only appear to come from F.
(iii) Our parents and teachers advise us to stay focussed. It implies that we concentrate all our energies at a single `"point"//"problem"` so that we can resolve the same easily. Staying focussed means we do not divert our energies and attention to several things at a time. This would lead us nowhere. Hence, the secret of success is to stay focussed.