Normal

If one line is normal to another, then it is at right angles.

In geometry, normal (a or the normal) refers to a line drawn perpendicular to and intersecting another line, plane or surface.

  • The way in which a normal appears in a geometric drawing depends on the circumstances:
    • When light strikes a flat surface or plane, or the boundary between two surfaces, the normal is drawn perpendicular to, so at a right angle (900) to the boundary.
    • When light strikes a curved surface or plane, the normal is drawn at a tangent to the boundary.
    • When light strikes a sphere in line with its centre of the sphere and passes straight through without deviation then the normal follows the same line.
Remember that:

Summary