What is a Magnetic Field

by Tega Jessa on September 29, 2010

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What is a Magnetic Field

Earth's magnetic field protects us from the solar wind. Image credit: NASA

A magnetic field is the area of influence exerted by a magnetic force. This field is normally focused along two poles. These poles are usually designated as north and south. However these directions are not the only two that a magnetic field can have. Most magnetic objects are composed of many small fields called domains. Here are some basic concepts of a magnetic field. The first real study of magnetism started during the 1600s and we are still trying to understand how the magnetic field works.

First a magnetic field can not be divided. A magnetic field will always be dipole which means it will have two poles. If you divide a magnet you will only get a smaller magnet with the same two poles. It will only change in its strength. If small enough a magnetic field can be turned around in its orientation by a larger magnetic filed. This is the reason why the domains in a ferromagnetic metal rarely orient in the same direction before being magnetized.

Second a magnetic field is the result of electric currents. An electric current is an electric charge moving in a defined path. This movement is what creates magnetic fields. The current can create a magnetic field as large as the Sun’s magnetosphere and as small as the domain of an atom. The important thing to know is that one is the companion of the other. Without an electric field you can’t have a magnetic field.

The next thing to be aware with a magnetic file is that opposites attract. Like poles in magnets will always repel each other while poles that are opposite in nature will attract each other. It is thanks to this phenomenon that scientist were actually able to diagram the lines of force.

So what is the importance of the magnetic field? The answer is that it is very vital to many aspects of life on earth. Because of its relationship with electricity we use it to produce and harness electrical currents in modern devices from blenders to power turbines. On the larger scale the Earth’s magnetic field called the magnetosphere helps to screen out the most harmful types of cosmic radiation. It also plays an important role in physics as the electromagnetic force is considered as one of the four fundamental forces in the known universe. Scientists are now looking to find a unified field theory that will properly explain the interaction between these forces.

We have written many articles about the magnetic field for Universe Today. Here’s an article about the Earth’s magnetic field, and here’s an article about Jupiter’s magnetic field.

If you’d like more info on Earth’s magnetic field, check out NASA’s Solar System Exploration Guide on Earth. And here’s a link to NASA’s Earth Observatory.

We’ve also recorded an episode of Astronomy Cast Questions Show about Magnetic Field. Listen here, Questions Show: Black Hole Surfaces, Magnetic Field Strengths and the Speed of Gravitons.

Wikipedia: Magnetic Field
Earth’s Magnetic Field

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