In the UK (and everywhere else, as far as I know), The basic
principles of Detroit Diesel Generators electricity is distributed
around the country in the form of alternating current. This
means that the flow of electrical current changes direction, usually
50 or 60 times per second. There are two reasons for this, both
historical.
First, electrical transformers (which we need to change
voltage, see below) only work with alternating currents. Second,
we generate electricity by spinning wires around inside magnets
(this is a bit of a simplification, of course), and this naturally
produces an alternating current. At the points where the current
is about to change direction, there will (for a short time) be no
current flowing at all. `Alternating current' is usually abbreviated
to `AC'.
The fact that current is alternating has
little practical impact on domestic wiring. If you grab a live conductor
you'll get a shock which is just as unpleasant even though, in principle,
part of the time no current will be flowing. One area where the
alternating nature of the electrical supply is apparent,
however, is in the use of fluorescent lights. Incandescent (filament)
bulbs generate their light because the filament becomes white-hot.
It cannot heat up and cool down as fast as the alternation of the
electrical current, so the light is fairly constant. Fluorescent
lights, on the other hand, produce a detectable flicker at the speed
of the supply alternation. The light from a fluorescent tube will
`pulse' about 100 times per second (50 times with the supply current
in one direction and 50 in the other).
We can't normally see this
flicker, but it does tend to make rotating machines look as though
they're standing still, or going backwards. This is why we are warned
not to use drilling equipment, for example, in strong fluorescent
light. |
