6C20.10 Poisson's Bright Spot

Concepts

Fresnel diffraction, wave-like properties of light

Diffraction Patterns & Fresnel Diffraction, Edge Diffraction
Diffraction Patterns & Fresnel Diffraction, Edge Diffraction
Diffraction Patterns & Fresnel Diffraction, Edge Diffraction
Diffraction Patterns & Fresnel Diffraction, Edge Diffraction

Overview

A laser beam is shone onto a ball bearing and a bright spot appears at the centre of the object’s shadow due to Fresnel diffraction.

Details

Equipment

  • [2] Slide with a small ball bearing
  • [1] Slide with a larger ball bearing
  • [1] Laser with beam expander
  • [1] Optical rail
  • [1] Slide mount
  • [1] Saddle
  • [2] Lab jack
  • [1] Extension cord (if necessary) 

Classroom Assembly

  1. Place the laser on top of the lab jacks, making sure the laser is pointed away from people.
  2. Place the slide mount on the optical rail and insert the sample slide to the slide mount.
  3. Plug in the laser and aim it at the ball bearing, make necessary adjustments such that the intended diffraction pattern is visible.
  4. Use the lab jacks to elevate the fringe pattern to a screen, if necessary.
  5. Turn off the laser.

Important Notes

  • Lasers can cause blindness. Use with caution.

Script

  1. Turn on the laser.
  2. Turn off the room lights to see the diffraction pattern more easily.
  3. Point out the bright spot in the centre of the shadow.
  4. Turn off the laser.

 

Additional Resources

References

  • PIRA 6C20.10

Disclaimer

  • Don't attempt this at home!

Last revised

  • 2017

Technicals

Related AV

Related demos

  • Pinhole Diffraction
  • Thin Wire Diffraction

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.