Define focus?

1.	Define focus?
Answer» When light rays coming from an object are parallel to principal axis and parallel to each other they strikes at mirror and after reflection they actually meet at a point on principal axis that point is called principal focus( or simply focus )of concave mirror.The focus of concave mirror is real hence when doing numericals arentaken as negative... Concave mirror:-If light rays coming parallel to the principal axis,strikes the mirror,then the reflected light rays meets at a point called focus.Convex mirror:-If light rays coming parallel to the principal axis, strikes the mirror, then the reflected rays appear to come from a point on the principal axis. This point is called focus. Concave mirror Of which mirror or lens

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