Magnetism Electricity: Theory of Electromagnetism
Electromagnets show that you can make magnetism using electricity. In fact, as European scientists discovered in the 19th century, electricity always makes magnetism when it moves about or changes. Every time an electric current flows in a wire, it generates a magnetic field all around it. Changing electricity, in short, produces magnetism.
As a consequence of Einstein’s theory of special relativity, electricity and magnetism are fundamentally interlinked. Both magnetism lacking electricity, and electricity without magnetism, are inconsistent with special relativity, due to such effects as length contraction, time dilation, and the fact that the magnetic force is velocity-dependent. However, when both electricity and magnetism are taken into account, the resulting theory (electromagnetism) is fully consistent with special relativity. In particular, a phenomenon that appears purely electric or purely magnetic to one observer may be a mix of both to another, or more generally the relative contributions of electricity and magnetism are dependent on the frame of reference. Thus, special relativity “mixes” electricity and magnetism into a single, inseparable phenomenon called electromagnetism, analogous to how relativity “mixes” space and time into spacetime.
The reverse is true as well: you can make electricity using a changing pattern of magnetism. That’s just as well or you wouldn’t be reading these words now. Virtually all the electricity we use (with the exception of electricity produced from solar cells) is made by devices called generators. These use powerful magnets and coils of wire to produce electricity with the help of turbines, devices that capture kinetic energy from fluids that move past them (typically wind, water, or steam made from coal, oil, or nuclear power).
How do you get electricity from magnetism? Simply speaking, you put a metal wire near a magnet (so the wire is inside the magnetic field). Move the wire or move the magnet so the magnetic field inside the wire fluctuates and electricity will flow through the wire. Keep moving the wire or magnet and you’ll make electricity continually.
In an antiferromagnet, unlike a ferromagnet, there is a tendency for the intrinsic magnetic moments of neighboring valence electrons to point in opposite directions. When all atoms are arranged in a substance so that each neighbor is anti-parallel, the substance is antiferromagnetic. Antiferromagnets have a zero net magnetic moment, meaning that no field is produced by them. Antiferromagnets are less common compared to the other types of behaviors and are mostly observed at low temperatures. In varying temperatures, antiferromagnets can be seen to exhibit diamagnetic and ferromagnetic properties.
You can see from this that electricity and magnetism are partners. Wherever you find one, the other is never far away. The first person to explain this properly, in the mid-19th century, was a brilliant Scottish physicist named James Clerk Maxwell. His theory summed up everything then known about electricity and magnetism in four relatively simple mathematical formulas. Maxwell’s equations, as we now call them, combined electricity and magnetism into a single, powerful theory we call electromagnetism. We now know that electromagnetism is one of the four fundamental forces that control everything that happens in our universe—and that’s a powerful idea indeed! Theory of Electromagnetism
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