Horseshoe magnet with north and south poles identified.
A magnetic field is an invisible field that exerts a magnetic force on substances that are sensitive to magnetism. A classic example is the field created by an iron magnet; To see how the energy works in such a field, a small magnet can be placed under a piece of paper and sprinkled with iron filings. As the filings respond to the magnetic field, they slowly orient themselves along an axis. Larger examples include Earth’s magnetic field and those created by other celestial bodies, such as stars and planets.
Electromagnet welded to a circuit board.
Many people think that magnetism is a property of metal, particularly iron, since common household magnets are made of iron. Electric currents are actually the force behind magnetic fields, which form as electric charges move. On a large scale, like an electromagnet, the field is created by passing current through wires. In the case of a house magnet, it is created by the movements of electrons in their orbits. Depending on the material and environmental factors, the strength of the field may vary.
Bar magnet with iron filings to illustrate the magnetic field.
Magnetic fields have many properties that have been used by scientists and others throughout the centuries. In navigation, ships can orient themselves with the help of the earth’s magnetic field, which, by the way, is several degrees from the geographical poles. In scientific research, these fields can be used to collect information about a location or object; Geologists, for example, use tools called magnetometers to measure environmental magnetism and learn more about rocks and underlying mineral materials.
MRI equipment uses magnetic fields.
Medicine uses it in diagnostic machines, such as magnetic resonance imaging (MRI) machines. In this case, the machine operator carefully generates and controls the field to collect information about the human body. In alternative medicine, some healers use magnets to achieve various desired effects. Scientists can also use other tools to create or alter magnetic fields to learn more about Earth.
Earth has a planetary magnetic field.
The strength of magnetic fields varies widely. An MRI machine, for example, can pull keys out of an unconscious doctor’s pocket, while a household magnet can be pulled out of a refrigerator door with little effort. There are also many different types of magnetic fields; an iron magnet, for example, exhibits ferromagnetism, while those created by an external current are known as electromagnetic fields.