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Invisible Glass

Bend light to make glass disappear

Australian Curriculum links

  • Science > Physical Sciences > Year 5 > ACSSU080

You’ll need

  • Large glass bowl or jar
  • Bottle of cheap cooking oil (e.g. canola or vegetable oil)
  • Small Pyrex glass bowl or jug which fits completely inside the large bowl

What to do

  1. Pour the oil into the large bowl until it is about 2/3 full.
  2. Immerse the Pyrex bowl in the oil (making sure it fills up with oil and is totally surrounded by it). Add extra oil if needed, until the smaller bowl is completely submerged.
  3. Look at the bowl from different angles. Can you see the smaller bowl inside? It should be invisible from some angles.

What’s happening?

The speed that light travels changes depending on what it is traveling through. It travels faster through air than through liquids or glass.

When light moves from one medium to another, it bends slightly, as well as changing speed. Even though glass is transparent, we can usually see a glass jars or bowls because the light that passes through it changes direction slightly, distorting our view of other objects we can see through the glass. A small amount of light bounces back (or reflects) off the glass too. Under normal circumstances, this combination of distortion and reflection tells our brain that we are looking at something transparent.

However, light travels at almost exactly the same speed through vegetable oil as it does through Pyrex glass, so as the light moves from the oil to the glass, it doesn’t change direction, and your brain has no way of knowing where the cooking oil ends and the Pyrex glass begins.