Concepts

Straight-line propagation of light

Overview

Chalk dust is spread in the path of a laser beam. The dust scatters light in the beam path, showing it moves in a straight line.

Details

Equipment

• [1] He-Ne Laser
• [1] Lab stand
• [1] 90-degree clamp
• [1] Chalk
• [1] Chalkboard brushes
• [1] Mirror

Classroom Assembly

1. Mount the laser on the lab stand, with the laser pointing to the side or far over the heads of students.
2. Plug in the laser.
3. Fill the brushes with chalk dust.

Important Notes

• Lasers can cause blindness. Use with caution.

Script

1. Turn off the lights.
2. Turn on the laser.
3. Clap the brushes together along the laser beam's path. Holding the brushes just underneath the beam works well.
4. [Optional] Hold a mirror in the beam path to show reflection of the laser beam.
5. Turn off the laser.
6. Turn on the lights.

Additional Resources