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Mirage in a cup

By David, 20 February 2020 Activity

Class of clear liquid with layers between the clear liquids, affecting the image seen through the glass.

You can see a mirage in a glass of sugary water.

If you’re in the desert on a hot day, you might see things that aren’t really there. But that’s not the only way to see a mirage – you can also see them in a glass of sugary water!

You will need

  • 3 glasses
  • Glucose syrup
  • Measuring cups
  • Fork or spoon for scooping and stirring
  • Masking tape and texta to make labels
  • Photo or magazine picture of a person

What to do

  1. Filling a glass with water from the tap.Fill one glass with warm (not hot!) water. Label this cup ‘water’.
  2. Label a second glass ‘glucose solution’.
  3. Measuring glucose syrup into a glass.Measure ¼ cup of glucose syrup into the glucose solution glass. Make sure you scrape out all the syrup from the cup measure!
  4. A glass containing 2 layers of clear liquid.Measure ¼ cup of warm water from the warm water cup into the glucose solution glass.
  5. Stitiing a glass of liquid with a fork.Stir the glucose and water until it is no longer cloudy and bubbles float to the top.
  6. Pour about half the glucose solution into the third glass. Don’t label this glass.
  7. Carefully pour water from the warm water glass into the glucose glass. You should be able to see the two liquids separately. Keep pouring until the amounts of water and glucose solution are about the same.
  8. Stir the glucose solution until it is thoroughly mixed.
  9. Hold the glucose solution glass in one hand and the third, unlabelled glass in the other hand.
  10. Pouring clear liquid from one glass to another.Tilt both glasses towards each other, and then very slowly, start pouring from the glucose solution glass into the unlabelled glass. Stop when the two layers of liquid are about the same height.
  11. Hold the warm water glass in one hand and the unlabelled glass in the other.
  12. Pouring clear liquid from one glass to another.Tilt both glasses towards each other, and then very slowly, start pouring from the warm water glass into the unlabelled glass. Stop when the three layers of liquid are each about the same height.
  13. A glass of clear liquid beside a mobile phone displaying a photograph of a person.Put the unlabelled glass in front of the picture of a person.
  14. Looking through layers of clear liquid in a glass at a photo. the images are multiple and some are turned upsidedown.Look through the glass at the picture, and move the glass and your head up and down. You should see multiple images of the person, some upside down and some right way up!

 

What’s happening?

Here’s a tricky science question: if air is clear and glass is clear, how do we see glass?

Clear substances let light pass through them, but they don’t leave that light unchanged. When light enters or leaves a substance, it bends. This doesn’t just let us see where we left that glass of water. It’s also the principle that makes a pair of glasses work!

In this activity, there are a lot of clear substances for light to enter and leave. Air, glass and the three different mixtures of liquids all bend light slightly differently. With so many layers, strange things appear – shapes are stretched or squished, and sometimes they even end up flipped upside down!

Real-life science

You can see similar effects in nature, too. On a very hot day, you might spot a mirage on the horizon. This is caused by a layer of hot air near the ground, which bends the light, making a slice of sky appear below the horizon. That sky can easily be mistaken for a pool of water!

However, this activity is closer to a much rarer phenomenon called Fata Morgana. Several layers of air, with cold layers near the ground and warmer ones above, create stacks of images above the horizon. These images can be squished, stretched or even flipped upside down. Fata Morgana has been the source of many stories of flying ships, islands that don’t exist and even UFOs.

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