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Unit 10: Electricity Page 26
you’re getting the two foil squares measured in amperes (A, or
to touch through the hole, and this amps). When electric current
is what really does it for your LED. passes through a material, it does
When you release it, the foil so by electrical conduction, but
spreads apart again because they there are different kinds of
are on opposite sides of the foam conduction, such as metallic
square. conduction (where electrons flow
through a conductor, like metal)
Bonus Idea: Stick just the sensor and electrolysis (where charged
under a rug and run longer wires atoms (called ions) flow through
from the sensor to your room. liquids).
When someone comes down the
Paper doesn’t conduct electricity –
hallway, they’ll trigger the sensor
it’s an insulator. The trip wire is an
and alert you before they get
NC (normally closed) switch,
there!
meaning that this circuit works
until you trigger the switch. So we
Experiment: Trip Wire
need a way to stop the current
Burglar Alarm
(flow of electrons) until we want
Burglar alarms not only protect the buzzer to activate.
your stuff, they put the intruder
When you stick the paper index
into a panic while they attempt to
card between the two tacks in the
disarm the triggered noisemaker.
clothespin, it breaks the electrical
Our burglar alarms are basically
connection and the switch goes in
switches which utilize the circuitry
the OFF position. Remove the
from Basic Circuits and clever
paper and your switch moves to
tricks in conductivity.
the ON position, and electrons are
flowing around and around your
A complete and exhaustive
circuit, and you hear a
description of electronics would
BUZZZZZZZZZ!
jump into the physics of solid state
electronics, which is covered in This alarm has a thin wire that
undergraduate university courses. someone "trips", which pulls out
Instead, here is a quick description the card, closes the switch, and
based on the fluid analogy for sounds a buzzer or lights up an
electric charge: LED!
The movement of electric charge is
called electric current, and is
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