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Q & A: Static and Moving electricity

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Most recent answer: 10/22/2007
Q:
If i run a wire from a electrostatic source like a vandegraff generator, isn’t it still static electricity no matter where or how far i run it ? couldn’t i put it through a coil and create magnetism ?
- frank hartman
st. lucie fl
A:
Hi Frank,

"Static electricity" is a name we use usually when electric charge builds up on some object and it therefore is at a high voltage. If there's a spark or other discharge (St. Elmo's fire, for example), we often say "it's the static electricity that does that" when in fact the charge is no longer static. While it sparks, the charges are in motion.

You can use a Van de Graaff generator to deposit charges on other objects, and wires can be used to move charge to and from a charged Van de Graaff generator. One warning. A wire tip is very sharp (usually), and electrons jump off of the sharp tip much more easily than off of a smooth, large, round sphere (which is the reason why Van de Graaff generators have those large spheres on their tops, and which is why lightning rods are sharp). This happens because the electric fields close to a sharp tip are much stronger than near a large sphere for the same voltage. You may find that with your wire, you may get sparks easily and not be able to put the full voltage of the Van de Graaff generator on the other object. It gets better if you connect the wire to something else that's smooth and round. If the wire is well insulated, then there should not be sparks along the length, and the tip will not spark if it is connected to an object at the same voltage.

If you then wind such a wire up in a coil, you won't get much of a magnet. The reason for this is that an electromagnet's strength depends on how much current goes through the windings. If the electric charge is static, then you won't get current and no magnetic field.

But: if you allow the Van de Graaff to discharge by sparking with this wire, and the wire is coiled up, then the very brief but very large amount of current will make a short pulse of magnetic field in the electromagnet. In fact, this is one way to make a strong, pulsed electromagnet. A coiled magnet resists a change in its current -- you need a big voltage to change the current -- and thus the magnetic field -- in an electromagnet very rapidly. A Van de Graaff is a good place to get such a high voltage.

Tom

(published on 10/22/2007)

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