Question:

A person is doing effort to locate the image of an object of a plane mirror by means of a ray-tracing diagram. The person draws a ray by the object which strikes the mirror at right angles to the surface of the mirror. Where does the ray depart from there?

Ans:

As-per to the law of reflection the angle of reflection is equal to the angle of incidence. In the case at hand the angle of incidence is zero. Therefore the angle of reflection must be zero meaning that the reflected ray travels along the normal. It was specified that the incoming ray was travelling toward the mirror along the normal as well as we have deduced that the reflected ray travels away from the mirror along the normal. Therefore the ray must reverse its direction at the surface of the mirror.