Historic Directions The ancient Greeks and Chinese knew about naturally magnetic stones called "lodestones. The Chinese discovered that they could make a needle magnetic by stroking it against a lodestone, and that the needle would point north-south.
Animal Magnetism Some animals, such as pigeons, bees, and salmon, can detect the Earth's magnetic field and use it to navigate. Scientists aren't sure how they do this, but these creatures seem to have magnetic material in their bodies that acts like a compass. The bright bands of color around the North Pole caused by the solar wind and the Earth's magnetic field. Also known as the aurora australis. The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit.
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Text on this page is printable and can be used according to our Terms of Service. Any interactives on this page can only be played while you are visiting our website. You cannot download interactives. A compass is a device that indicates direction. It is one of the most important instruments for navigation. Students create and observe ferrofluids to understand magnetic field lines and how they can affect planets.
Students learn how the sun's activity and magnetism drive space weather and impact Earth's living and technological systems. Join our community of educators and receive the latest information on National Geographic's resources for you and your students. Skip to content. This explains why breaking a magnet in half creates two smaller magnets with north and south poles.
It also explains why opposite poles attract -- the field lines leave the north pole of one magnet and naturally enter the south pole of another, essentially creating one larger magnet. Like poles repel each other because their lines of force are traveling in opposite directions, clashing with each other rather than moving together.
To make a magnet, all you have to do is encourage the magnetic domains in a piece of metal to point in the same direction. That's what happens when you rub a needle with a magnet -- the exposure to the magnetic field encourages the domains to align.
Other ways to align magnetic domains in a piece of metal include:. Two of these methods are among scientific theories about how lodestone forms in nature. Some scientists speculate magnetite becomes magnetic when struck by lightning.
Others theorize that pieces of magnetite became magnets when the Earth was first formed. The domains aligned with the Earth's magnetic field while iron oxide was molten and flexible. The most common method of making magnets today involves placing metal in a magnetic field. The field exerts torque on the material, encouraging the domains to align.
There's a slight delay, known as hysteresis , between the application of the field and the change in domains -- it takes a few moments for the domains to start to move. Here's what happens:. The resulting magnet's strength depends on the amount of force used to move the domains. Its permanence, or retentivity , depends on how difficult it was to encourage the domains to align. Materials that are hard to magnetize generally retain their magnetism for longer periods, while materials that are easy to magnetize often revert to their original nonmagnetic state.
You can reduce a magnet's strength or demagnetize it entirely by exposing it to a magnetic field that is aligned in the opposite direction. You can also demagnetize a material by heating it above its Curie point , or the temperature at which it loses its magnetism. The heat distorts the material and excites the magnetic particles, causing the domains to fall out of alignment.
Large, powerful magnets have numerous industrial uses, from writing data to inducing current in wires. But shipping and installing huge magnets can be difficult and dangerous. Not only can magnets damage other items in transit, they can be difficult or impossible to install upon their arrival. In addition, magnets tend to collect an array of ferromagnetic debris, which is hard to remove and can even be dangerous. For this reason, facilities that use very large magnets often have equipment on site that lets them turn ferromagnetic materials into magnets.
Often, the device is essentially an electromagnet. If you've read How Electromagnets Work , you know that an electrical current moving through a wire creates a magnetic field. Moving electrical charges are responsible for the magnetic field in permanent magnets as well. But a magnet's field doesn't come from a large current traveling through a wire -- it comes from the movement of electrons. Many people imagine electrons as tiny particles that orbit an atom's nucleus the way planets orbit a sun.
As quantum physicists currently explain it, the movement of electrons is a little more complicated than that. Essentially, electrons fill an atom's shell-like orbitals , where they behave as both particles and waves.
The electrons have a charge and a mass , as well as a movement that physicists describe as spin in an upward or downward direction. You can learn more about electrons in How Atoms Work. Generally, electrons fill the atom's orbitals in pairs. If one of the electrons in a pair spins upward, the other spins downward.
It's impossible for both of the electrons in a pair to spin in the same direction. This is part of a quantum-mechanical principle known as the Pauli Exclusion Principle. Even though an atom's electrons don't move very far, their movement is enough to create a tiny magnetic field. Since paired electrons spin in opposite directions, their magnetic fields cancel one another out.
Atoms of ferromagnetic elements, on the other hand, have several unpaired electrons that have the same spin. Iron, for example, has four unpaired electrons with the same spin. Because they have no opposing fields to cancel their effects, these electrons have an orbital magnetic moment.
The magnetic moment is a vector -- it has a magnitude and a direction. It's related to both the magnetic field strength and the torque that the field exerts. A whole magnet's magnetic moments come from the moments of all of its atoms. In metals like iron, the orbital magnetic moment encourages nearby atoms to align along the same north-south field lines. Iron and other ferromagnetic materials are crystalline.
As they cool from a molten state, groups of atoms with parallel orbital spin line up within the crystal structure. This forms the magnetic domains discussed in the previous section. You may have noticed that the materials that make good magnets are the same as the materials magnets attract.
This is because magnets attract materials that have unpaired electrons that spin in the same direction. In other words, the quality that turns a metal into a magnet also attracts the metal to magnets. Many other elements are diamagnetic -- their unpaired atoms create a field that weakly repels a magnet. A few materials don't react with magnets at all. This explanation and its underlying quantum physics are fairly complicated, and without them the idea of magnetic attraction can be mystifying.
So it's not surprising that people have viewed magnetic materials with suspicion for much of history. You can measure magnetic fields using instruments like gauss meters , and you can describe and explain them using numerous equations. Here are some of the basics:. Every time you use a computer, you're using magnets. A hard drive relies on magnets to store data, and some monitors use magnets to create images on the screen.
If your home has a doorbell , it probably uses an electromagnet to drive a noisemaker. Magnets are also vital components in CRT televisions , speakers , microphones , generators, transformers, electric motors , burglar alarms , cassette tapes, compasses and car speedometers. In addition to their practical uses, magnets have numerous amazing properties. They can induce current in wire and supply torque for electric motors.
A strong enough magnetic field can levitate small objects or even small animals. Maglev trains use magnetic propulsion to travel at high speeds, and magnetic fluids help fill rocket engines with fuel. The Earth 's magnetic field, known as the magnetosphere , protects it from the solar wind. According to Wired magazine, some people even implant tiny neodymium magnets in their fingers, allowing them to detect electromagnetic fields [Source: Wired ].
Magnetic Resonance Imaging MRI machines use magnetic fields to allow doctors to examine patients' internal organs. Doctors also use pulsed electromagnetic fields to treat broken bones that have not healed correctly. This method, approved by the United States Food and Drug Administration in the s, can mend bones that have not responded to other treatment. Permanent magnets are magnets with permanent magnetic fields.
They cannot be turned off, nor can their fields be increased or decreased easily. These are items that are almost always magnetized. There are a few ways to remove a magnetic field from a permanent magnet.
One of these methods requires increasing the temperature of the magnet. This adds heat and energy to the system which will take away the magnetic field.
The temperature at which the magnet no longer holds its field is known as the Curie point. Another way to make a magnet lose its magnetic field is by hitting it. The impacts on the magnet will ruin the needed configuration of the electrons and the magnetic field will weaken and possibly be lost.
The other group is called temporary magnets. This category includes items that are magnetic, but do not contain their own magnetic fields.
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