Question

Deline the principal focus of a concave mirror.
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Answer 1

ANSWER:

The principal focus of a concave mirror is a point on the principal axis of the mirror where the light rays seem to be diverging out from.

Or,

When parallel beams of light are incident on the reflecting surface of the concave mirror, they seem to diverge out from a point. The light rays on extending them backwards tend to meet at a point on the principal axis of the mirror. This point is known as the principal focus of the concave mirror