What happens to the electricity when the cord is
unplugged? Why doesn't the electricity spill out?
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
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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Update: June 2012