The Science of Magnetism
by Laurisa White Reyes
Ever wonder how a compass works? Or why two magnets held together can push each other away? Or why some things are magnetic and others aren’t?
Magnetism is a force that attracts or repels at a distance. Magnets attract certain metallic substances such as nickel, cobalt and iron. Most other substances (i.e. wood, cotton, plastic) are not magnetic. If you were to walk around your house with a magnet and touch it to different objects, you will find that the magnet will “stick” to some things and not others. This article will explain why this occurs.
How Magnets Work
Every magnet has two poles, North and South, just like the Earth. Each magnet is surrounded by a magnetic field, the area within which the magnetic force is exerted. To determine a magnet’s magnetic field, place a small amount of iron shavings on a piece of white paper and place a magnet beneath the paper. The shavings will align themselves in a pattern around the magnet outlining the magnetic field.
Magnetic force is similar to an electrical current. Electrical currents flow from a positive to a negative charge. Magnetic field lines “flow” from North to South. On a single magnet, these lines will travel from the North pole and loop around to the South pole. Place two magnets close together, the North pole of one magnet will seek out, or attract, the South pole of the other. In other words, opposite poles attract (N ↔ S) while like poles repel (N ↕ S). If you were to break a magnet in half, each half would have both a North and South pole. This explains why two magnets attract each other, but how can a magnet attract an object, such as an iron nail, that is not magnetized?
Iron contains magnetic domains, atoms with North and South poles. In an unmagnetized piece of iron, these domains exist randomly. When it is placed within a magnetic field, however, the force of the magnet (seeking the South pole) will cause these domains to line up so that the iron becomes temporarily magnetized. When the iron is pulled away from the magnet, the domains become random again.
The Discovery of Magnetism
The Ancient Greeks and Chinese observed magnetism in Iodstones (natural magnets). They found that when allowed to rotate freely, these Iodstones would always point in a north-south direction. They applied this attribute of Iodstones to navigation and building.
In 1293, a Frenchman named Pierre de Maricourt discovered that iodstone magnets had two poles, North and South, but it took another three hundred years before someone realized that the Earth itself was a giant magnet with North and South poles. In 1820, scientists discovered that electricity and magnetism are related. Later, Pierre Currie (husband to Marie) found that magnets lose their magnetism above a certain temperature, now known as the Curie Point.
Magnetic experimentation continued into the 20th century as scientists began studying the behavior of electrons. The study of how magnetism affects atoms and molecules is called “Quantum Mechanics.” American physicists, Edward Purcell and Flix Bloch, developed a way to measure the magnetic field of the nuclei of atoms. This discovery enabled medical researchers to develop the MRI, Medical Resonance Imaging, a form of imaging that can detect abnormalities within the human body.
In the late 20th century, scientists also created superconducting materials, powerful magnets used in nuclear research.
The Earth’s Magnetic Field
The Earth behaves like a giant magnet, though scientists are not certain why. Like any other magnet, the earth exerts a magnetic force that “flows” from the magnetic North pole to the magnetic South pole. These poles actually differ from the geographical poles, pointing away from the geographical poles, which means a compass never points to true North. This difference between the north of a compass and true North is called “magnetic declination.”
The Earth’s magnetosphere can be observed in magnetic storms and the polar aurora, called the “Northern Lights”, visible in places like Alaska and Norway. Satellites experience radiation belts and other disturbances caused by the Earth’s magnetism. The Earth’s magnetic field extends to as far as 64,000 kilometers into space. There is evidence that the Earth’s magnetic field has actually reversed itself at least twenty times.
Types and Uses of Magnets
There are three types of magnets: Permanent magnets, temporary magnets, and electromagnets.
Permanent magnets are the type of magnets we think of as magnets. They retain their magnetism indefinitely. Permanent magnets come in many shapes and sizes, bar-shaped, horseshoe, round, etc. Temporary magnets are magnets that act like permanent magnets but eventually lose their magnetism. Nails, paper clips, or other soft-iron items can be temporarily magnetized. I mentioned earlier that electricity and magnetism are related. Electromagnets are temporary magnets caused by electrical current. When the current is on, the object is magnetized. When the current is off, the magnetism disappears. These electromagnets play an important role in all our lives today. Electromagnets are used in all electric motors and these motors run everything from refrigerators, vacuum cleaners, blenders, cassette recorders, DVD players, racecars, and more! Electromagnets are used in industry for fax machines, cranes, and power plant generators.
Trains, elevators, and subways all use electromagnets. Even the scientific and medical industries use them. Magnets have become such a common part of our lives, we couldn’t imagine life without them!
Make Your Own Magnet:
Items you will need:
☐ 1 Permanent magnet
☐ 1 or more soft-iron objects such as paperclips or nails
Hold the paperclip or nail firmly between your thumb and forefinger. With your other hand, grip the permanent magnet and hold it to the end of the paperclip or nail. Draw the magnet from one end of the object to the other in one direction. Remove the permanent magnet. The paperclip or nail will now act like a magnet until its magnetism fades. Use it to attract other paperclips, thumbtacks, iron filings, etc.
For a list of experiments you can construct to demonstrate magnetism, visit Magnet Man at
http://my.execpc.com/~rhoadley/magindex.htm. L.W.R. ■