1. Magnets 1 Two poles of the opposite kind attract each other. Two poles of the same kind repel each other.

2. Field lines 2 In the early 1800’s, Michael Faraday notes that iron filings line up around a magnet to show “force field lines”. The lines show the direction of force on a north pole.

3. Electromagnets 3 In 1820 Hans Christien Ørsted discovers that an electric current in a wire creates a magnetic field. This is the principle behind the electromagnet.

4. Lorentz force 4 In 1892 Hendrick Lorentz discovers that a current-carrying wire feels a force when it is in a magnetic field. This is the principle behind the electric motor. The force on the current is perpendicular to the magnetic field and perpendicular to the current. (If the current is in the same direction as the field, there is no force.) The force on the electrons is out of the page. Why did it take him so long???