6A40.30 Matching Index of Refraction with Light Pipes


Refractive index, refraction


A U-rod is capable of transmitting a laser beam between the two ends of the rod like an optical fibre. Therefore when a laser pointer is pointed at one end of the rod, the other end of the rod glows. When the rod is submerged in mineral oil, however, the laser beam is no longer transmitted to the other end. This is because the U-rod and mineral oil have the same index of refraction and the U-rod does not behave like an optical fibre anymore.



  • [1] U-rod
  • [1] Laser pointer
  • [1] Glass container
  • [1] Bottle of mineral oil
  • [1] Roll of paper towels

Classroom Assembly

  1. Pour the mineral oil to the glass container.


  1. Without submerging the U-rod in mineral oil, direct the laser beam to one end of the rod.
  2. Notice the glow on the other end of the rod.
  3. Lower the rod into the container until it is submerged in mineral oil.
  4. Notice the intensity of the glow decreases as the rod is lowered.


Additional Resources


  • PIRA 6A40.30


  • Don't attempt this at home!

Last revised

  • 2017


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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.