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Question:
What happens to the electricity when the cord is unplugged? Why doesn't the electricity spill out?



Replies:
Electricity must have a complete uninterrupted loop in order to flow. This loop is called a circuit. Any time you unplug something, you break the loop and electricity cannot flow. A switch on the wall does the same thing: it makes the loop when it is on and breaks the loop when it is off. Nothing really happens to the electricity when you unplug a cord. It is still there waiting for a loop to be created so that it can flow further.


That's a good question. Electricity flows, in many ways, like water, and in fact many of the equations describing electrical circuitry are very similar to the equations decribing fluid flow. The main difference between the ways electricity and water flow is that electricity needs a conductor. You see, electricity is the movement of electrons, which are very small particles containing negative electric charges. Since electrons are negatively charged, they need to be near to other particles containing positive electric charges. In a conductor, such as a metal, the electrons can move around freely in the spaces between the nuclei of the metal atoms, which are positively charged. The electrons can't easily go outside the metal, because they don't want to be far away from the positive nuclei. Substances that are poor conductors of electricity also contain electrons in the vicinity of positive nuclei, but the electrons are more tightly-held instead of shared. Any electrons coming in can't find a decent place to be - the electrons already there won't move aside as easily as in a metal.

Also, electricity doesn't just flow out of an outlet like water flows out of a faucet. To maintain charge balance, that is, to keep electrons near positive nuclei at all times, electrons have to flow in a circuit. This means that when electrons flow away from one part of a circuit, other electrons have to flow toward that part. (The only time you can get around this rule is when objects build up static charges - too many or not enough electrons. Then electrons can flow from something with a negative charge [too many electrons] to something with a positive charge [too few electrons] without needing to flow back.) What is actually happening when something is plugged into an electrical outlet is that electrons are flowing out through one terminal and back through the other. (In fact, the direction reverses 60 times a second, which is why it's called "alternating current.")

So, the reason electrons don't spill out of an electrical outlet is that (1) electrons can't move through air as well as through metal, and (2) there would be no place for them to go if they did.

Richard Barrans Jr., Ph.D.



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