A ray of light is incident on a totally reflecting surface (mirror) at a certain point. This point is called point of incidence. If we draw a line which is perpendicular to the reflecting surface at the point of incidence, this line is called the normal. it is an imaginary line perpendicular to the surface reflecting the light.When an incident ray strikes normally to any reflecting surface then the reflected ray will trace back the incident ray. Hence, angle between incident ray and reflected ray is 0 0 .