Magnetism

What is magnetism? The term magnetism stems from certain rocks called lodestones from more than 2000 years ago in the region of Magnesia in Greece. The Chinese were the first to use magnets. They used magnets as early as the 12 th century in navigating ships.

General Properties of Magnets A magnet suspended from a thread and allowed to swing freely will always line up in a north-south direction. Therefore, a compass is nothing more than a small magnet. The end that points toward the north is identified as the “North Pole” and the other is the “South Pole”.

General Properties of Magnets Two like poles repel and opposite poles attract. Magnets always have two opposite poles. The magnetic south pole (south pole of the earth-magnet) must be near the geographic north pole.

Magnetic Field Surrounding the Earth

Permanent vs. Temporary Magnets A magnet can cause other materials to become magnets through polarization. During polarization all of the electrons in a group of neighboring atoms are all aligned in the same direction. (called a domain) When the material is not in a magnetic field, the domains tend to point in random directions. In a temporary magnet, the domains return to their random arrangement when the external field is removed. In a permanent magnet, the domains remain aligned after the external field is removed. Only a few elements are capable of becoming permanent magnets: iron, cobalt, nickel, neodymium, and gadolinium.

Magnetic Fields Forces between magnets occur not only when the magnets are touching, but also when they are held apart. Magnetic forces can be described by the existence of magnetic fields around magnets. Magnetic fields are vector quantities. As with an electric field, the strength of a magnetic field increases as the distance from the magnet decreases.

Magnetic Field Lines

Electromagnetism Electric currents produce magnetic fields. The strength of the magnetic field is proportional to the current in the wire and varies inversely with the distance from the wire. The magnetic forces are perpendicular to the direction of the current in the wire. A long wire consisting of many loops is called a solenoid. The field from each loop adds to the others and creates a greater total field strength. This type of magnet is called an electromagnet. Increasing the number of loops increases the strength of the field. Increasing the voltage of the energy source can also increase the strength of the magnetic field.

Advantages of an Electromagnet Electromagnets can be turned on and off by controlling the electric current. The strength of an electromagnet can also be altered by altering the magnitude of the current.

Electromagnetic Induction A changing magnetic field can produce an electric current. To produce an electric current, either the conductor can move through a magnetic field or the magnetic field can move past the conductor.

Applications of Magnetism Do a quick Google search of each of the following topics and learn how each topic relates to magnetism. Aurora Borealis Maglev trains MRI machines Solar Storms