Optics
6A40.30b: Disappearing Beaker
Description: This demonstration shows that an object with the same index of refraction as a liquid will look transparent when immersed in it.
Equipment:
- Lots of wesson vegetable oil
- A large pyrex beaker with as few markings as possible
- A small pyrex beaker with as few markings as possible
- Paper towels
Setup Procedure:
- Spread a few paper towels down where this demo will be used.
- Fill the large beaker up with wesson vegetable oil, taking into account that the small beaker will also be going in later (so don't fill it up all the way).
- When the professor is finished, pour the vegetable oil back into the main wesson container.
- You will need to clean the pyrex beakers out with soap and water.
Demonstration Procedure:
- Show students the large pyrex beaker. Explain that it has Wesson vegetable oil in it.
- Show them the small pyrex beaker. Fill it up with the wesson oil.
- Lower the small beaker into the large beaker, and note that it "disappears".
- This is because the index of refraction of pyrex and wesson vegetable oil is about the same.
- Since the light does not bend, it's as if there is nothing there, which makes it seem like there is only oil.
- A video camera can be used for lage classes. Point the camera at the side, since from the top the lid of the small beaker can be seen eaiser.
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