Normal line - Flat mirrors
To understand any further information you have to relate to the normal line in connection with flat mirrors.
There are several definitions of the normal line of a flat mirror.
Normal line is the line perpendicular (at 90°) to the mirror.
The normal line is an imaginary line at 90° to where the ray touches the mirror surface.
But at Mammoth Memory we believe that the image you should think of is a bow held by a Norman warrior in which the bow is the curve and the arrow is the normal line.
Although the bow in our case is a flat mirror you can still see that the normal line is at 90° to the bow or the mirror as follows:
In order to find the reflected ray you must first draw the normal line which is a line drawn perpendicular (at 90°) to the mirror at the point where the ray of light touches the mirror.
We can now draw the reflected ray because we know the angle of incidence (`thetai`) is equal to the angle of refraction (`thetar`).