Whether you are trying to build your own generator, are an electronics hobbyist or are just looking for a science fair project, you should learn how to build electromagnets. Electromagnets are simple devices that mimic the behavior of natural magnets, with one important difference. Unlike natural magnets, electromagnets can change their magnetic field strength. Varying any of the four basic elements of an electromagnet will allow you to set it to whatever strength you desire, for whatever purpose you desire.
Number of Loops
An electromagnet is made out of a coil of wire wrapped around a metal core—usually iron--and connected to a battery. As the electrical current moves around the loops of the coil, it generates a magnetic field like that of a small bar magnet. It has a north pole on one side of the loop and a south pole on the other. Because the coil is made out of one continuous wire, the magnetic fields of each loop “stack up,” creating something like a large bar magnet. One way to increase or decrease the strength of the magnetic field is to change the number of loops in the coil. The more loops you add, the stronger the field will become. The more loops you remove, the weaker the field will become.
The Metal Core
The metal inside the coil magnifies the field created by it. Changing the metal core for a different metal will make the electromagnet stronger or weaker. Iron cores make for very strong fields. Steel cores make weaker fields. Neodymium cores make the strongest fields. Sliding the core partially out of the coil will weaken the field, because less of the metal is within it.
Changing the battery voltage will also change the field the electromagnet produces. The higher the voltage of the battery, the more current will flow through the coil. The greater the current in the coil, the stronger the magnetic field will grow. Conversely, lowering the battery voltage decreases the current, therefore weakening the field.
Although metal wires are very efficient conductors of electricity, they still have some resistance to the flow of current. Using larger gauges of wire on the coil will decrease this innate resistance. This will increase the current and therefore the field. Using smaller gauges will increase the resistance, reduce the current and weaken the field. Using different types of metal wire will also affect the field strength, because every metal has a different inherent resistance to current.