What is a Magnetic Field?

Horseshoe magnet with north and south poles labeled.
Electromagnet soldered to a circuit board.
MRI equipment uses magnetic fields.
Bar magnet with iron filings to illustrate the magnetic field.
The Earth has a planetary magnetic field.
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  • Written By: Mary McMahon
  • Edited By: Bronwyn Harris
  • Last Modified Date: 11 September 2014
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A magnetic field is an invisible field that exerts a magnetic force on substances that are sensitive to magnetism. A classic example of one is the field created by an iron magnet; to see how the energy in such a field works, a small magnet can be placed under a piece of paper and iron filings sprinkled on it. As the filings respond to the magnetic field, they will slowly orient themselves along an axis. Larger examples include the Earth's magnetic field, and those that are created by other celestial bodies such as stars and planets.

Many people think of magnetism as a property of metal, particularly iron, since common household magnets are made from iron. Electrical currents are actually the force behind magnetic fields, which form as electrical charges move around. On a large scale like an electromagnet, the field is created by passing current through wires. In the case of a household magnet, it is created by the movements of electrons in their orbits. Depending on the material and environmental factors, the strength of the field can vary.


Magnetic fields have many properties that scientists and others have used over the centuries. In navigation, ships can orient themselves with the assistance of the Earth's magnetic field, which is, incidentally, located several degrees off the geographic poles. In scientific research, these fields can be used to gather information about a location or object; geologists, for example, use tools called magnetometers to measure ambient magnetism to learn more about the underlying rock and mineral materials.

Medicine uses it in things like diagnostic machines such as Magnetic Resonance Imaging (MRI) equipment. In this case, the field is carefully generated and controlled by the operator of the machine for the purpose of gathering 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 for the purpose of learning more about the Earth.

The strength of magnetic fields varies widely. An MRI machine, for example, can pull the keys out of an unwitting doctor's pocket, while a household magnet can be knocked from the refrigerator door with little effort. There are also many different types of magnetic fields; an iron magnet, for example, displays ferromagnetism, while those created with the use of an external current are known as electromagnetic fields.


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Post 25

What can interrupt an electromagnetic senor? Some background: "smart parking meters" use transmitters which sense ferrous material above (car's engine block) then transmit to the meter. When the car pulls away, the meter resets. However, these meters have high fail rate for re-setting while a car is still parked there. What type of material (moving along the sidewalk) would trigger the meter to re-set?

Post 24

How can a magnetic field be in the corner of my basement? If I walk toward this corner I feel like I am standing in front of a large TV set and getting the electricity off it.

Post 16

Can wood or certain timber types alter or have influence to change a magnetic field in anyway enhanced by vibration, i.e. a guitar pickup coil?

Post 15

Is there any evidence of magnetic or force field from an animal- specifically a bird? Today, when I held a piece of food in front of the beak of my canary, I felt resistance in the air space about one inch between the food I held and his beak.

It was similar to the reverse magnetic field between two magnets but much weaker than the magnets. I definitely felt something because I did it more than once.

I am wondering if somehow this is theoretically possible, or is it just my imagination. Is there any record or reports of similar experiences?

Post 14

Sorry, that's a really bad explanation. I think the idea is what IS a magnetic field. I know the flow of electrons creates a magnetic field, but with a flow, interrupt that, and you have available energy. That would suggest a magnet would be a battery. Not so.

Question still stands. What is a magnetic field, and further, how fast does it propagate" (not the field establishing), but the "Invisible force".

Could go all the way, and ask what is gravity? (11 dimensions nws)

Many thanks, TTYL

Post 13

What are some examples of magnetic energy's effect on weather?

Post 12

Like, where is the magnetic field located? In the middle or sides or all around?

Post 9

what is the working of simple dc motor?

Moderator's reply: wiseGEEK has an article that may help you out...

Post 8

Can you make a magnet spin continuously by copying the design of a simple dynamo?

Post 6

what exactly comes out of the north pole of a magnet and enters the south pole?

Post 3

Great website and ideas!!!! Helped me with my science fair!!!!

Post 2

can u give me some examples of magnetic energy?

Post 1

great website thanks for the help. really helped in my hw. but just wanna ask what exactly are the uses of the earth's magnetic field for animals and humans?

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