Magnetism
In the lesson on DC electricity, you saw that magnetism was used to create electricity with a DC generator. Now, you've seen a magnet attract a piece of iron to it, but what does that have to do with creating electricity?
This gets you curious, and you may have other questions to ask, such as:
- What are some of the properties of a magnet?
- How can you detect magnetism?
- What does electricity have to do with magnetism?
- How can you create a magnet?
- How can you create electricity with a magnet?
Properties of a magnet
Just about everyone has seen or played with a magnet. It is a special type of metal that attracts iron, steel, and other magnets. It can also repel the similar end of another magnet.Magnetism is safe
While electrical charges can give a person a shock or even kill the person, magnetism doesn't seem to have any harmful effects, as far as we know.In fact, there are people who claim that magnets are even beneficial to your health. There are companies that sell magnetic materials to attach to your body to help relieve chronic pain. I am not sure whether those devices really work or not, but at least they don't seem to harm the people by exposing them to magnetism.
Magnets attract iron
A magnet is an object made of a material that attracts iron and steel, as well as a few other metals. It also both attracts and repels other magnets.The force that attracts and repels two magnets is a force that acts at a distance called magnetism or magnetic force.
Magnet has two poles
The opposite ends of a magnet are called its north and south poles. In reality, they should be called the "north seeking" and "south seeking" poles, because they seek the Earth's North Pole and South Pole, respectively.
Electric charges and magnetism similar
Just as the two types of electrical charge that attract each other, the two poles of a magnet that attract each other. In electricity like charges repel, and in magnetism like poles repel. That means if you put the north pole of a magnet near the north pole of another magnet, they will push apart, just like when you put a negatively charge object next to one that also has a negative charge.Electric charges and magnetism different
Every magnet has a north pole and a south pole. A positive or negative electrical charge can stand alone, but a magnet always has a N and S pole.If you cut a magnet in half, each piece will still have a N and S pole.
Detecting a magnetic field
You have seen how magnets attract certain metals. That is one easy way to detect if an object is magnetic. But what if the magnetic field is not strong enough to cause a piece of iron to be attracted? There are some other ways to detect a magnetic field or its force.Iron filings on a piece of paper
By spreading fine iron filings or dust on a piece of paper laid on top of a magnet, you can see the outline of the magnetic lines of force or the magnetic field, similar to those drawn in Figure 1 above.This experiment also shows that magnetism will act through many materials, such as paper. Would the experiment work if a sheet of iron was used to sprinkle the filings? What about aluminum foil?
The compass
A great invention to detect small magnetic fields is a compass. It is simply a thin magnet or magnetized iron needle balanced on a pivot. The needle will rotate to point toward the opposite pole of a magnet. It can be very sensitive to small magnetic fields.Since it is a small magnets, usually a compass has one end marked N and the other marked S.
Earth is a huge magnet
The compass was used to discover that the Earth is a huge magnet. The north compass needle will always point toward the north.It would be more appropriate to call the N or north side of the compass the the "north seeking" pole. Since the north end of the compass is attracted toward the north, the earth-magnet is really the S pole at the Earth's north pole. That is confusing, and it is similar to the problem concerning the direction of electrical current versus the direction of the electrons in DC electricity.
Electricity creates a magnetic field
Another discovery from the compass was that electricity creates a magnetic field. If you put a wire near a compass and pass a current through the wire, you can see the compass needle move because of the magnetic field produced by the current.If an electric current creates a magnetic field, then perhaps it could be used to create a magnet.
Creating a magnet
You can create a magnet by magnetizing a piece of iron or steel or by using electricity to make an electro-magnet.Magnetize a steel needle
You can magnetize a piece of steel by rubbing a magnet in one direction along the steel. This lines up the atoms in the steel, so it acts like a magnet. The steel often won't remain magnetized, while the true magnet is permanently magnetized.If you use soft iron or steel, such as a paper clip, it will lose its magnetism quickly. Also, you can disorient the atoms in a magnetized needle by heating it or by dropping the needle on a hard object.
The electromagnet
Since electric current creates a magnetic field, perhaps you could use that property to make a magnet. Suppose you wrapped the wire around a piece of iron, such as a nail. When electricity was sent through the wire, the nail will become highly magnetized. You can verify that by picking up small objects or by showing its effect on a compass.This invention was called the electromagnet.
Try making an electromagnet with a battery, wire and a nail.
Creating electricity with a magnet
Now if electric current moving though a wire can cause a magnetic field, could just the opposite—a wire moving through a magnetic field—cause electric current? The answer is yes.If you take a N and S magnet and pass a wire through their magnetic field, electric current will flow through the wire.
Inventions using electromagnets
The discovery of electromagnetism opened the door for numerous, important inventions.Pick up and drop things
What is interesting about the electromagnet is that when you turn off the electricity, the magnetism is also turned off. Thus, you could use an electromagnet to pick up a piece of iron and then drop it someplace else.This property is used in junk yards, where they use huge electromagnets and a crane to pick up and move old, junked cars.
Loud speaker
The loud speakers in your radio use electromagnets to create sound. The electronics in the radio turns the electric current on and off at an extremely fast rate. This moves the loud speaker membrane or cone back and forth, resulting in sound and even music. Take a look at a loud speaker and see the coil of wire and electromagnet in its back area.Phonograph
The grooves in a phonograph record causes the needle to vibrate. Electronic amplifies the signal and rapidly turns the current to the loud speaker on and off. This results in playing of the sound that was previous recorded into those grooves.Electric motor
An electric motor is an even more clever application of electromagnets. Suppose you put some electromagnets on a wheel and put some permanent magnets around the wheel. The electromagnets could be made to attract and repel the surrounding magnets, causing the wheel to turn. Look at an electric motor and see the internal wheel made of electromagnets and the outer shell made of permanent magnetic material.Reversing inventions
An amazing principle that you will see many times in science is that of the duality of concepts, or that you can reverse ideas. For example, consider some of the inventions using magnetism. What would happen if we would reverse those inventions?For example, since electricity can cause magnetism, is it possible to use magnetism to create electricity?
Electric motor creates electricity
If you took an electric motor and spun the rotor, its wires would cut through the magnetic fields and create electricity. An electric generator is simply an electric motor that you are spinning.