Why the Beaker Disappear in the Oil

Have you ever read The Emperor’s New Clothes by Hans Christian Andersen? Two weavers make clothes for the king, the cloth which is invisible to ones who are either unfit for his position or "hopelessly stupid". Are there any objects invisible in reality? This magic like experiment will teach you how to make an object disappear. Sound crazy, isn’t it?

Age: 3+         Time: < 10mins

 Safety 

1. Adult supervision.
2. Be careful with the fragile glassware.
3. The oil can make the floor very slippery.

 Materials List 

• Cooking oil (such as peanut oil, etc.),
• 500ml beaker
• 100ml beaker
• Glass rod (optional)
• Glass pipette dropper (optional)

 Instruction 

Step 1/2 – Pour 400ml of cooking oil in the 500ml beaker.


Step 2/2 – There are three ways to have fun with it.
1. Completely submerge the 100ml beaker in the cooking oil and the small beaker will disappear.












2. With the index finger, block the button end of the pipette and put another end vertically into the oil. The pipette can be clearly seen at this moment. When you release your index finger, you will see that the pipette will slowly disappear from the bottom to the top of the oil.

                         

 Troubleshooting 

Why this experiment cannot apply to the daily used glassware?

— Different glassware has different refractive indices. It is recommended to use high borosilicate glass, such as beakers and conical flasks.

 Question to Ask 

1. Where did the "disappeared" beaker go?
2. If there are air bubbles in the beaker, will the beaker still visible?
3. Do you know which liquid can make the glassware ’disappear’?

 Scientific Description 

When light travels from one transparent medium into another, the direction of propagation generally will change. This phenomenon is called the refraction of light. the refractive index or index of refraction of a material is a dimensionless number that describes how fast light travels through the material.  The higher the refractive index of the material, the stronger the ability to refract light. When the refractive index of the two materials is different, the light will travel in a different direction in them. The refractive index of the glass is greater than the refractive index of water so the boundary between the beaker and the water can be clearly seen. When two transparent stuff shares the same refractive index, the direction of the travelling light in them is the same so when one is placed in another one, the boundary disappears and that is why it comes to disappear. In this experiment, the refractive index of the oil is almost the same as that of the glass, when the glass beaker is placed in the oil, the boundary is almost invisible. The glass rod and the pipette in the oil share this invisible magic.

 Extensions 

Hide the glassware such as the beaker in the oil, and then take out the pieces one by one. That is what magic does.

 Disposal 

The oil can be reserved for the next experiment. Wash the glassware with washing soap. Be careful with the fragile glassware.