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you have learnt in the text how Huygens principle leads to the laws of relfection and refraction. Use the same principle to deduce directly that a point object placed in front of a plane mirror produces a virtual image whose distance from the mirror is equla to the distance of the object from the mirror. |
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Answer» Solution :In Fig. P is a POINT object PLACED at a distance `r` from a PLANE mirror `M_(1), M_(2)`. With `P` as centre and `PO = r` as radius, draw a spherical arc , `AB`. This is the spherical wavefront from the object, incident on `M_(1),M_(2)`. If mirror were not present, the position of wave front `AB` would appear as`P"B"`, according to huyghen's construction. As is CLEAR from the figure, `A'B'` and `A"B"` are two spherical arcs located symmetricallyon either side of `M_(1) M_(2)`. Therefore, `A'PB'` can be treated as reflected image of `A"PB"`. From simple geometry, we find `OP = OP'`. which was to be proved. 
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