question_answer 13)

You have learnt in the text how Huygens'principle leads to the laws of reflection andrefraction. Use the same principle to deducedirectly that a point object placed in front ofa plane mirror produces a virtual imagewhose distance from the mirror is equal tothe object distance from the mirror. 

Answer:

                Let there be a point object A at a distancey from a plane mirror. Treating this pointto be spherical source of light, we canassume spherical wave fronts progressing from A of radius. Let there be no mirror then after time the wave front will reachA' as wavefront I. If a mirror is placed asshown in the figure then image will beformed at A' represented by II. It is seen that OA' = OA i.e. reflectedimage is formed at a distance equal to thedistance of object from the mirror.