10.13 You have learned in the text how Huygens’ principle leads to the laws of reflection 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 equal to the object's distance from the mirror.

Hint: Recall the Huygens principle.
Step: Deduce the given relation.

Let an object is placed at O in front of a plane mirror. MO′ at a distance r (as shown in the given figure).

                               

the circle is drawn with center (O) such that it touches the plane mirror at point O′. According to Huygens' Principle, the wavefront of Incident light is XY. If the mirror is not present, then a similar wavefront X′Y′(as XY) would form behind O′ at distance r (as Mown in the given figure).

                            

we can consider X′Y′ a virtual reflected ray for the plane mirror. Hence, a point object which is placed in front of the plane mirror produces a virtual image whose distance from the plane mirror is equal to the object distance (r).