High School Teachers at CERN
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Peter Dunne - UK

Measuring magnetic fields by comparison

You need a large U-shaped magnet of about 0.1 tesla. Give a pupil a soft iron bar and ask them to hold it between the poles and remember how much effort it takes to hold it steady. They then put the iron bar into other fields and estimate how much easier or harder it is to hold steady. The field from a small bar magnet should elicit responses such as "a thousand times smaller….." while the Earth's field should be undetectable.

An extension is to place the bar into the field produced by a 240 turn coil with a small current passing through it; it is not very impressive but adding two transformer C-cores produces a strong field that is so strong the cores cannot be pulled apart.
 

A quick and memorable demonstration of the Lorentz force

Loosely lay a wire between the poles of the U-shaped magnet. Connect the ends of the wire to a 12V power supply (i.e. short circuit it) and watch as the wire leaps out of the magnet. Disconnect!
 

Modeling the X ray diffraction pattern of DNA using a lightbulb filament

Take a torch bulb (e.g.2.5V, 0.2A) and carefully place it in a bench vice. A careful squeeze will allow the glass cover to be removed without destroying the filament. The filament is a coiled coil. Shining a laser through it will produce an diffraction pattern showing the X that signifies a helix structure. Try stretching the filament to show out which bits of the pattern depend on which bits of the target.

A good introduction to this may be to shine the laser through cut-outs of letters of the alphabet. See the Revised Nuffield Advanced Physics Student and Teachers' Guides (Book 2, Unit J) for details and photographs of this activity.