Posted on 14 February 2012 at 14:09h

This morning I was explaining polarisation to my SL class. Went through the usual examples of measuring the concentration of sugar solution and the old 7 segment display neither of which really succeeded in waking up the class.

Maybe 3D films will do the trick?

Well I don't have a 3D smart board so couldn't actually show a 3D film but I tried to explain how two images were projected each with a different direction of polarisation. The special glasses have lenses with corresponding polarisation directions so each eye sees a different image giving the illusion of 3D. Obviously it's much better to be able to see this in action so I decided to improvise by covering my projector with one piece of polaroid and handing the other to a student who looked at the board whilst rotating it. I think Tiange was just being kind when she reported that the screen went dark and bright because when I tried there was no difference. It appeared that the light became unpolarised when it reflected off the screen. Looking directly at the projector worked fine but not the screen. This sort of ruined my explanation of how 3D film works so it was back to the SMART board.

What I found out was that reflection off insulators does mess up the polarisation but refection off metals doesn't, thats why 3D cinemas have special metallic screens. I tried hanging a piece of aluminium foil on the SMART board and it worked a treat as you can see. Notice how the screen doesn't change much but the foil does.

I was going to try this with the 3D glasses I got when I saw Harry Potter (no not the Harry Potter lookalike versions) but discovered that the this type of film (Real D) uses circularly polarised light which is something much more complicated. This means that you don't have to sit with your head at the same angle throughout the film. I wish someone had told me that. It might have prevented the stiff neck.