Magnetic Force Help
As children, most of us discovered that magnets “stick” to some metals. Iron, nickel, and alloys containing either or both of these elements are known as ferromagnetic materials . Magnets exert force on these metals. Magnets generally do not exert force on other metals unless those metals carry electric currents. Electrically insulating substances never attract magnets under normal conditions.
Cause And Strength
When a magnet is brought near a piece of ferromagnetic material, the atoms in the material become lined up so that the metal is temporarily magnetized. This produces a magnetic force between the atoms of the ferromagnetic substance and those in the magnet.
If a magnet is near another magnet, the force is even stronger than it is when the same magnet is near a ferromagnetic substance. In addition, the force can be either repulsive (the magnets repel, or push away from each other) or attractive (the magnets attract, or pull toward each other) depending on the way the magnets are turned. The force gets stronger as the magnets are brought closer and closer together.
Some magnets are so strong that no human being can pull them apart if they get “stuck” together, and no person can bring them all the way together against their mutual repulsive force. This is especially true of electromagnets , discussed later in this chapter. The tremendous forces available are of use in industry. A huge electromagnet can be used to carry heavy pieces of scrap iron or steel from place to place. Other electromagnets can provide sufficient repulsion to suspend one object above another. This is called magnetic levitation .
Electric Charge Carriers In Motion
Whenever the atoms in a ferromagnetic material are aligned, a magnetic field exists. A magnetic field also can be caused by the motion of electric charge carriers either in a wire or in free space.
The magnetic field around a permanent magnet arises from the same cause as the field around a wire that carries an electric current. The responsible factor in either case is the motion of electrically charged particles. In a wire, the electrons move along the conductor, being passed from atom to atom. In a permanent magnet, the movement of orbiting electrons occurs in such a manner that an “effective current” is produced by the way the electrons move within individual atoms.
Magnetic fields can be produced by the motion of charged particles through space. The Sun is constantly ejecting protons and helium nuclei. These particles carry a positive electric charge. Because of this, they produce “effective currents” as they travel through space. These currents in turn generate magnetic fields. When these fields interact with the Earth’s geomagnetic field, the particles are forced to change direction, and they are accelerated toward the geomagnetic poles.
If there is an eruption on the Sun called a solar flare , the Sun ejects more charged particles than normal. When these arrive at the Earth’s geomagnetic poles, their magnetic fields, collectively working together, can disrupt the Earth’s geomagnetic field. Then there is a geomagnetic storm . Such an event causes changes in the Earth’s ionosphere, affecting long-distance radio communications at certain frequencies. If the fluctuations are intense enough, even wire communications and electrical power transmission can be interfered with. Microwave transmissions generally are immune to the effects of geomagnetic storms. Fiberoptic cable links and free-space laser communications are not affected. Aurora (northern or southern lights) are frequently observed at night during geomagnetic storms.
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