Polarisation

Science Museum Hands-On Learning

Last week we went to the Science Museum in London.  They had an activity where you could learn about polarisation.

Normally light travels or enters our eyes in lots of different directions.  Polarisation is a special type of vision that makes light only be able to come in one way.  Special polarised glasses only let the light in from one direction.

For this activity I needed cellotape and a clear piece of plastic.  I cut strips of cellotape and made a pattern.

This is Finn's pattern.

Then we put our designs on a special light table and put on polarised glasses.  This is my brother Patch looking through polarised glasses at the pictures on the light table.

When light passes through a raindrop in the sky, it breaks up the light into all the different colours that we don't usually see.  The cellotape in this experiment works just like the raindrops, and then we use the glasses to polarise the light.

The demonstrater had some popsicle sticks stuck together.  It was her example of what polarisation was like.  It was like a gate letting some light waves through in one direction, but blocking others.

If you look super closely at this picture you can see a fish.  The back end is covered by the polarising glasses but the other end isn't.  Can you see the difference?

This is my picture.  I experimented with making 3D with the cellotape by making bumps.  I also used one of the drawing techniques that I had learnt at school and did some feathering with tiny pieces of tape.

And here is my picture under the glasses.

HOW DO 3D GLASSES WORK?

When we got home we learned some more about polarisation.  We learned that the glasses you use when you see 3D movies are actually polarised.

This is because each eye sees an object only in 2D.  And each eye sees an object from a slightly different angle.  In real life, then our brain puts the 2 pictures together making it 3D.

To have the same effect in a movie there has to be wall between the eyes to make sure that each eye sees a slightly different picture with no overlap.  But you can't build a wall between your eyes!!  So polarised glasses have 2 different lenses that each let light in in a different way.  So the movie would have 2 layers one for each eye to see.

One way to do that is like the gate the demonstrater showed us.  One lense would only let in vertical light waves (up and down)  and the other lense would let in horizontal light waves (side to side).  But this doesn't work very well if you move your head.

So now lots of glasses use 'circular polarisation' where one eye sees light moving clockwise and the other sees light waves moving anti-clockwise.