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Name: Kate M.
Status: student
Age: 16
Location: N/A
Country: N/A
Date: 8/26/2004

I no that by running current though a coil of wire you create an magnetic field (electromagnet) but what is the principle behind this? Why does this happen?

Dear Kate,

Whenever charges are moving they produce a magnetic field as well as the electric field which they always produce. The magnetic field can be detected and shown to be different from the electric field because it produces a force only on moving charges,. You may ask "moving with respect to what?" Good question. That question played a large role in leading Einstein to the special theory of relativity.

Those are the basic principles behind magnetism. If you are asking why those are the principles, I can only say that physics cannot answer such questions. We can describe magnetism and calculate its effects, but do not know why the laws of magnetism have exactly that form. It is true, of course, that almost any change would make the universe unlivable, but that's a reason for the form the laws have only if you think that the universe was designed just for mankind. It does rather look that way!

I am not sure I answered your question. Feel free to ask again if you would like more information.

Best, Dick Plano Professor of Physics emeritus, Rutgers University

Kate M.,

Electromagnetism is based on two basic properties of matter: electric charge produces electric field, motion of electric charge produces magnetic field. This electric field goes out from or in to the charge, depending on whether the charge is positive or negative. The magnetic field loops around the direction of motion. Electric current is many electric charges moving together through a wire. All the small magnetic fields add together to produce strong magnetic fields around the wire.

Dr. Ken Mellendorf
Physics Instructor
Illinois Central College

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