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   More on Magnets

Anyone who has played with magnets knows they have two poles, north and south. Opposite poles pull each other, while like poles push away. These forces of push and pull drive all electric motors, including electromagnetic guns.

The idea behind these guns is deceptively simple. Magnetic push removes friction by levitating a projectile above a track. Other electromagnets push it out the barrel, pull it out, or combine push and pull.

There are two basic kinds of magnets. Permanent magnets are made of a material such as iron in which each individual atom or molecule is a tiny magnet. Normally these materials don’t act like magnets because the pole of each atom points in a random direction, and this cancels out their magnetic forces.

You can turn an iron nail into a permanent magnet by repeatedly stroking it in the same direction across a magnet. Each stroke makes a tiny twist to the poles of its iron atoms toward the same direction. The more they point in the same direction, the stronger the nail magnet becomes.

Electromagnets line up the poles of these atoms using a different principle: an electrical current creates a magnetic field. Place iron into a magnetic field, and the field twists its atoms in the same direction, boosting the field by a factor of thousands. Children [doomed to grow up to be engineers] often play with this principle by wrapping coils of an insulated wire around an iron nail. Hook up the wire to a battery and, voila! A darn good electromagnet.

You can control the strength and shape of an electromagnet’s field by controlling the electrical current and by the design of the wires through which it flows. More turns to the coil or higher current increase the field. Desktop toys such as the rotating levitated space shuttle below use electromagnets. Although permanent magnets could levitate this toy, only electromagnets can make it rotate, as well.
floating space shuttle -- uses magnetic forces
Magnetically levitated rotating shuttle from the Edmund Scientific catalog.

This seeming simplicity – flip a switch, push and pull – has inspired gun enthusiasts for over a century. However, as so often happens, engineering realities have hampered their hopes.

There are two basic kinds of magnets. Permanent magnets are made of a material such as iron in which each individual atom or molecule is a tiny magnet. Normally these materials don’t act like magnets because the pole of each atom points in a random direction, and this cancels out their magnetic forces.

You can turn an iron nail into a permanent magnet by repeatedly stroking it in the same direction across a magnet. Each stroke makes a tiny twist to the poles of its iron atoms toward the same direction. The more they point in the same direction, the stronger the nail magnet becomes. Warning – this takes a loooong time.

Now the thing about permanent magnets is you can’t make them strong enough for a superweapon. The maximum strength is limited by the basic nature of the magnetic materials from which magnets are made. The strongest of them are made of alloys of some very rare members of the Periodic Table of the Elements.

The strongest of all, with a magnetic flux density of 1.5 Tesla, is called the neodymium magnet, although in reality neodymium is only a small part of the magnet (chemical formula: Nd2Fe14B, meaning two atoms of the element neodymium (Nd), fourteen of iron (Fe) and one of boron (B)). Now 1.5 Tesla (15,000 Gauss) is hugely powerful, 1,500 times more than a refrigerator magnet.

Why Building Super Strong Magnets is Hard to Do

Getting more strength with an electromagnet, while possible, is really, really difficult. Yet we need more than 1.5 Tesla to build an electromagnetic gun that will be more powerful than a conventional rifle or cannon.

Here’s why it’s so hard to top 1.5 Tesla. Electromagnets line up the poles of these atoms using a different principle than a permanent magnet. Any electrical current creates a magnetic field. Place iron into a magnetic field, and the field twists its atoms in the same direction, boosting the field by a factor of thousands. Children [doomed to grow up to be engineers] often play with this principle by wrapping coils of an insulated wire around an iron nail. Hook up the wire to a battery and, whoopee! It’s now an electromagnet.

Here’s why we end up having a hard time getting past 1.5 Tesla.  As you increase a magnetic field, the enhancing effect of even the best core material, soft iron, eventually turns against the engineer, blocking any further increase in the magnetic field. In practice, ~1.7 tesla is the highest magnetic field that any iron-core electromagnet will permit. OK, that’s better than a neodymium magnet, but only a tiny bit better.

One solution is to replace iron with air. Fine, except that now, in order to compensate for loosing the assistance of iron, is that we must boost the electrical current and/or increase the number of turns in the conductor coils of the electromagnet by about 20,000. This is impractical because the amount of wire becomes to bulky. The other solution is to increase the current by the same factor, or increase both by a lesser, but still gigantic, amount.

That Darned Periodic Table of the Elements and Superconductivity--->>

Back to how to build electromagnetic guns --->>

 

 
       © 2013 Carolyn Meinel