2.1 Electromotive Force
The key points of the section on magnetism are:
- In the 1970s, the chief way of making electricity was to use mechanical energy to create electrical energy through magnetism (as opposed to batteries, which converts chemical energy into electrical energy). It probably still is.
- We think of a magnet creating a magnetic field with lines of magnetic force around it. If you pour iron fillings around a magnet, you can see the lines of force (see diagram below).
- Another name for lines of force is lines of flux.
- The section presents six basic rules of magnetism. The first is that magnetic lines of force always form closed loops.
- Another rule is that magnetic lines of force pass through all kinds of material.
- A third is that they always try to form the smallest loops possible.
- Magnetic lines of force have a polarity. They leave the north pole of a magnet and return into the south pole. (Inside the magnet, they move from south the north, much as with batteries.)
- They enter and leave the magnetic poles at right angles, perpendicular.
- Like magnetic polarity repels, unlike attracts. So a north pole is attracted to a south pole, but repelled by another north pole.
- The measure of a magnetic field is its flux density.
- Some materials are more attracted by magnets than others. Magnetic materials distort the more usual form of a magnetic field.