B1 Intermediate 1836 Folder Collection
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Hi, I'm Ross, and today I'm going to be showing you the secret to making things invisible.
So this is something which you can do at home.
It's really easy and a great trick to show your friends.
But I assure you, it's not magic, it's all science.
If you place a test tube into a beaker of water, you can still see the test tube,
despite the air, the water, and the tube all being transparent.
This is because as the light passes from one material to another,
it changes speed and direction, allowing you to see the edges of the tube.
But if the angle of the light changes, objects can appear distorted.
Watch what happens to this picture on the other side the glass as we add water to it.
This is known as refraction.
As the lens of your eye changes shape, it allows you to focus on objects at different distances as it refracts the light.
Understanding this concept has led to the invention of lenses in glasses, cameras, and telescopes.
But what if we change the water for something else? Different materials have different refractive properties,
so if we switch the water for something which has the same refractive index as the glass,
the light will appear to pass straight through without changing speed or direction.
For your invisibility trick you'll need some Pyrex glass,
so any measuring cyclinders or coffee pots which are made of Pyrex will be great for this.
And you'll also need something called glycerol.
So, glycerol is a sweetener that you can get from the local chemist,
It's also known as 'glycerine'.
I'm going to be wearing some gloves for this because it can get pretty sticky.
You don't have to use glycerol though...
If you can't find any glycerol, then don't worry - baby oil, or vegetable oil will work just as well.
Here I have a beaker full of glycerol, and if I take a Pyrex test tube,
and place it in to the beaker - we can still see it
because of the air in the tube. But if I dip it just beneath the surface...
... it vanishes!
So the pyrex and the glycerol have the same the refractive index,
meaning the light can pass straight through
without being refracted.
This is a bit awkward - I've just dropped it in. Um... hold on let me see if I can get it back out.
There we go. I'll pull that out of there. Hold on there's something else in here as well.
Another one...
And, another one...
Hang on. There's something else... If I can just grab it and...
So there we go, this beaker has been hidden inside this big jar of glycerol the entire time!
Did you manage to spot it? Let us know if you did.
So there we have it, the science of light and refraction, give it a go at home
and tweet us to let us know if manage to fool any of your friends with this invisibility trick.
For more science to try at home,
check out Sarah and David investigating the sciences of sweets.
Or, if you'd like to see more about how your eyes work,
why not watch an eyeball dissection? And for more science every week
click subscribe. Thanks for watching.
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How to make something invisible | Do Try This At Home | At-Bristol Science Centre

1836 Folder Collection
Cheng-Hong Liu published on February 20, 2015    Joyce Ching-Hsuan Liu translated    Blair reviewed
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