# 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.

or

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).