Magnetism

What is magnetism? The word magnet comes from a magnetic stone called a loadstone found in Magnesia Greece. These loadstones were attracted to each other and certain metals. Magnets are similar to electric charges. They have a north and south pole like charges have positive and negative charges. Like charges, opposites attract and like poles repel. Unlike charges, that can be separated and kept as a positive or negative charge, you cannot separate the poles of a magnet. If you break a magnet in half you only get two magnets, each with their own set of north and south poles.

What makes a magnet? Magnets are made of regions in the metal called domains. The domains are filled with clusters of atoms that are polarize (have a north and south pole). The domains are aligned with all or most north poles facing in the same directions, likewise with the south poles. The more alignment in the domains, the stronger the magnet. Most objects are not magnetize and their domains are facing every which way. Domains

Magnetic fields Iron filings sprinkled on a sheet of paper over a bar magnet will tend to trace out a pattern of lines that surround the magnet. The space around a magnet, in which a magnetic force is exerted, is filled with a magnetic field. The shape of the field is revealed by magnetic field lines. Notice the lines want to connect between the north and the south pole of the magnet. This is what causes the attraction of the opposite poles and repulsion of like poles.

The nature of a magnetic field Magnetism is very much related to electricity. Just as electric charges are surrounded by an electric field, when it is moving, it creates a magnetic field. The magnetic field is caused by distortions in the electric field when the charge is moving. Where is the motion coming from in a stationary magnet? The electrons in an atom are in constant motion and thus all atoms are like little tiny mini magnets. Clustering them with the same orientation makes the domains we talked about earlier. Electrons spinning in the same direction make a stronger magnetic field but spinning in the opposite direction they cancel each other out. This is why most matter is not magnetic and cannot be magnetized. Iron is a substance whose spinning electrons do not cancel eachother out and this is the material most magnets are made from. Nickel and cobalt do as well, but not as much as iron.

Making a piece of iron magnetic The difference between a piece of ordinary iron and an iron magnet is the alignment of domains. In a common iron nail, the domains are randomly oriented. When a strong magnet is brought nearby, there is a growth in size of domains oriented in the direction of the magnetic field. The domains also become aligned much as electric dipoles are aligned in the presence of a charged rod. When you remove the nail from the magnet, thermal motion causes most of the domains to return to a random arrangement. Permanent magnets are made by simply placing pieces of iron or certain iron alloys in strong magnetic fields. Another way of making a permanent magnet is to stroke a piece of iron with a magnet. The stroking motion aligns the domains in the iron. If a permanent magnet is dropped or heated, some of the domains are jostled out of alignment and the magnet becomes weaker.

Looking at magnetic field lines with a compass The Red end of a compass is pointed to the north pole and that means our north pole is really a south pole since a magnet attracts the opposite pole. (if using an arrow to depict a compass, the arrow head is always attracting to a south pole)

The earth’s magnetic field Because the earth has an iron-nickel core that spins independent of the crust of the earth, it generates a magnetic field around the earth A compass aligns with the earth’s magnetic field. So if you could walk from north pole to south pole, the compass needle would not move. This magnetic field deflects ionizing radiation from the sun and space and protects us from exposure to them. It also makes the northern lights,

Creating a magnet with electrical current The magnetic field surrounding a current-carrying conductor can be shown by arranging magnetic compasses around the wire. The compasses line up with the magnetic field produced by the current, a pattern of concentric circles about the wire. When the current reverses direction, the compasses turn around, showing that the direction of the magnetic field changes also. When there is no current in the wire, the compasses align with Earth’s magnetic field. When there is a current in the wire, the compasses align with the stronger magnetic field near the wire.

If the wire is bent into a loop, the magnetic field lines become bunched up inside the loop. If the wire is bent into another loop, the concentration of magnetic field lines inside the double loop is twice that of the single loop. The magnetic field intensity increases as the number of loops is increased. Arrow goes from North pole to South pole

Electric Currents and Magnetic Fields If a piece of iron is placed inside the coil of an electromagnet, the magnetic domains in the iron are induced into alignment, increasing the magnetic field intensity. So, electromagnetic induction occurs when a magnetic field exists near a conductor like iron. When the electromagnet comes close to another iron source, the magnetic field of the magnet induces a magnetic field in the other iron source, making it temporarily magnetized. What happens when you switch the wires on the battery and cause the current to run the other way through the coils? The poles of the electromagnet switch.

Electric Motors Just like an electric current can induce a magnetic field, a magnetic field can induce an electric field. If you spin a magnet in a coil of wires, you can cause a current to flow through the wire. This is how electric power plants work. The electricity flows into the motor and changes electric energy into mechanical energy There are 2 kinds of current that can be induced. DC or direct current: current flows in one direction AC or alternating current: current’s direction flows in alternating directions. This is what is made with electric power plants.

Transformers A transformer is used to change the voltage in the electricity that enters your house. The electric company sends it’s electricity through the electric wires at very high voltage because it has to travel long distances. The high voltage is too much for the appliances you use in your house. The transformer is used to lower the voltage from the electric company to your house where you can safely use it.