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Solenoids

 If the iron core of an electromagnet is not fixed, but able to slide in and out of the coil, you a have a device called a "Solenoid". {R.10.160}{R.42.351} If the iron core is pulled halfway out of the coil and current is applied, the magnetic force will pull the iron into the center of the coil. This action is used for many things in the world around us, like door and alarm bell ringers, to actuate some types of relays, and to engage the starter motor in your car (to name just a few).

 To make your own solenoid, wind about 60 turns of 24 gauge wire around a drinking straw (You might want to insert a dowell or piece of pencil into the straw to prevent it from being crushed). The coil should be wound in about 3 layers of 20 turns each. Insert a small nail into the end of the straw, so that the tip of the nail is just inside the beginning of the coil. When you connect a "C" cell battery, the nail will be pulled into the center of the coil. Note that you might have to slightly adjust the starting position of the nail.

 If the current is applied to the solenoid coil for a very short time (like a 10th of a second) and removed, and there are no protrusions to stop it, the iron core will be shot out the other end of the coil. This is the basis of operation for a linear induction engine.

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© 1998, Robert Lyon Richards