not just described, Explained


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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.

Try Why Do Astronauts Float by Julian Hamm

This gives you space to place apparatus, for example a fine-beam tube.

back to Lesson 8: Atoms 2: Electrons