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How To Do a Refraction Demonstration with Vegetable Oil

How To Do a Refraction Demonstration with Vegetable Oil

Now it’s there, now it’s not!

In this short video, Emma Dent shows you a quick refraction demonstration with a boiling tube and a beaker of vegetable oil.

Ideal for GCSE students, this refraction demonstration shows if the refractive index of the glass is similar to that of the vegetable oil, the bending of light may be minimal, and the glass may appear less visible or “disappear” when immersed in the oil.

Why does the glass disappear in the vegetable oil?

If you place the boiling tube full of air into a larger pyrex beaker full of vegetable oil you will be able to see the smaller beaker due to the different indexes of refraction. However, if you fill the tube with the oil, it will seemingly disappear because they now have basically the same index of refraction.

This is because light travels through the glass filled with vegetable oil and vegetable at the same speed, so your eyes don’t see a boundary where the tube is, rendering it invisible.



You will need:

  • Boiling tube
  • Vegetable oil
  • Glass beaker



  1. Fill a transparent container (the glass beaker) with vegetable oil.
  2. Place a boiling tube into the vegetable oil.
  3. Pour vegetable oil into the boiling tube.
  4. Observe how the glass object may seem to partially or fully disappear due to the refractive index matching between the glass and the vegetable oil.

All health and safety measures are the responsibility of the teacher doing the demonstration. A thorough risk assessment should be carried out and guidance procedures followed. It is suggested that you practice before demonstration in front of a class.

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