Bending cathode rays with an electromagnet
What is an electromagnet?
An electromagnet is any coil of wire with an electric current flowing through it.
An electromagnet has several advantages over a permanent magnet. You can change its strength by changing the current flowing through it and you can create a uniform magnetic field, whose size you can calculate.
Helmholtz coils
In the middle of a coil the spacing of the magnetic field lines stays fairly constant. This shows that the field is uniform there. You can pull the two ends of the coil apart to make ‘Helmholtz coils’ and the field stays constant in the middle.
Animations showing the magnetic field produced by a coil of wire and how this can be shaped using Helmholtz coils.GCSE Maths exam soon?
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This gives you space to place apparatus, for example a fine-beam tube.