Scan a Laser

What path does yonder laser take?

laser scanned by hand into a mirror



A scanned dot of laser light can show the path that light takes when it reflects from a mirror.


A pointer Laser.
Plexiglass mirrors, flat and curved, 4" high or more.
2 large binder clips.
A white table or white paper covered table.


Use the binder clips to mount the plexiglass mirror so that it stands vertically over a white table surface.

To Do and Notice

Hold the laser in your hand and point the beam at the table.
Move your wrist to make a point of laser light move along the table surface.

Place a flat mirror so that it is perpendicular to the table surface.

Hold the laser above and in front of the mirror and rotate the laser so that the point of light moves along the table and hits the mirror.

Notice how the dot of light moves toward the mirror then bounces off of it.

Move your wrist faster and slower to show the bounce of a dot of light or a line of light.

Move your hand so that the dot of light moves into the mirror at an angle, notice that the reflected dot leaves the mirror at the same angle.


Place two mirrors so that the dot of light reflects first off one mirror and then off the other.


Place a concave curved mirror on the table.

Move the dot of laser light so that it collides with the curved mirror.

Send in a beam parallel to the axis of the mirror. Notice that all such beams reflect from the mirror and then pass through the focal point of the mirror.

(The axis of the mirror is a line perpendicular to the center of the mirror.)

Send beams through the focal point.

Notice that all beams that pass though the focal point exit parallel to the axis of the mirror.

Send light through any other point (further from the mirror than the focal point) to the mirror. Notice that the light goes through another point called the image point.

What's Going On?

When light reflects from a mirror it reflects so that the angle of reflection from a piece of the mirror is equal to the angle of incidence.


The illusion produced by scanning the dot of laser light is that a slow motion packet of light bounces off the mirror.

Draft Activities

Scientific Explorations with Paul Doherty

© 1999

21 Feb 99