6A02.35 Laser and Chalk Dust


Straight-line propagation of light


Chalk dust is spread in the path of a laser beam. The dust causes light scattering in the beam path, rendering it visible.



  • [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.


  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


  • PIRA 6A02.35


  • Don't attempt this at home!

Last revised

  • 2020


Related AV

Related demos


If you have any questions about the demos or notes you would like to add to this page, contact Ricky Chu at ricky_chu AT sfu DOT ca.