Polarisation explored

What the Activity is for

Connecting polarisation to the everyday.

There are a number of standard laboratory demonstrations of polarisation, from those performed with 3 cm waves, through to those relying on pieces of Polaroid. These can be incorporated, but the focus of the activity here is to show how polarisation is a part of everyday life.

What to Prepare

• some polarising filters
• a pair of polarising sunglasses
• some LCD displays
• an analogue radio, with aerial, definitely FM and AM
• a television aerial
• a sheet of reflecting glass, a light sensor and a focused light source
• a 3 cm transmitter–receiver pair

What Happens During this Activity

You might start with one of the standard demonstrations of polarisation, perhaps with a 3 cm transmitter– receiver pair. If either of these is rotated then the signal detected drops to nothing – it's really rather impressive. At this level we recommend not introducing the polarising grid unless this helps to explain what is going on with some of the later examples. So don't introduce it yourself, but have it to hand in case it's useful for the conversations that evolve.

After that it is perhaps best to go to a practical and challenging situation, which may have happened to the children already, of looking at LCD displays through polarising sunglasses. You might introduce this with a question, or a story. This will probably involve trying to read a GPS (satnav), a mobile phone screen, a digital camera screen or perhaps an e-reader screen. These might be more accessible contexts than the time-worn angler peering into the lake.

The point to make is that there is something funny going on that depends on angle. Here, making sense of the phenomenon depends on students already being familiar with the idea of polarisation – either through experiment, which you may have covered above, or through a theoretical approach, perhaps using the interactive provided in the physics narrative of this topic.

Images of rows of terraced houses, all with their television aerials aligned, are particularly useful to introduce the idea that other electromagnetic waves might also be polarised. Having a television aerial – actually in your hand – allows you to use your hands as well as your voice to bring alive the idea that the vibrations will be detected in one plane only. Much the same point can be made by using a radio with an aerial that can easily be angled. You'll need to practice in the laboratory where you are to carry out this demonstration in order to be sure that you can gain and lose a particular station by rotating the aerial. (The same station is often broadcast at different polarisations from different transmitters).