Heisenberg's Uncertainty Principal and Diffraction

Interactive Lecture using a Laser Demo and a Computer Simulation (60 minutes)
Diffraction is usually taught as classical wave behaviour and left as that. However, electrons, photons and other individual quantum objects show this behaviour so there must be a quantum mechanical explanation. The explanation comes from Heisenberg's Uncertainty Principal. This lesson starts with a really great, cheap hands-on demonstration of diffraction using a couple of pencils and a laser pointer. Then the diffraction is explored quantitatively using four slits of known width. Next, diffraction is examined particle by particle using a simulation of single slit diffraction with photons, electrons and pions. The students need a copy of the HUP worksheet. Details of the lesson and the answers to the worksheet can be found in the teacher's notes.

This lesson involves lasers which have safety concerns that you should be aware of.

You might want to watch a short video of MIT Professor Walter Lewin from 32 to 42 minutes. He goes through the explanation of HUP and diffraction but in a teacher-centered rather student-centered fashion.

Last Updated April 2009