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If you have ever had someone work on the electricity in your home or
school, you know that the first thing the electrician does is turn off
the power. That's so he or she does not accidentally become part of a
circuit! In order for electricity to move from one location to the next,
it has to travel along a conductive material, such as copper. Conductive
materials permit the electrons to move fairly freely. See if you can create
a complete circuit using the following materials.
- 2 flashlight
batteries (D size)
- Some small
gauge electrical wire (cut in pieces about 30 cm long)
- A flashlight
light bulb
- Electrical
tape
- Some modeling
clay
- Steel
wool
Begin by connecting the electrical wire to the light bulb. Tape the exposed
copper end of the wire to the metal side of the bulb. Place the exposed
end of another wire on the surface of a lump of clay (a 3 cm cube will
be sufficient). Press the bulb into the clay so that the bottom of the
bulb is firmly in contact with the exposed end of the wire. Tape the other
end of one of the wires to the flat side of the battery (the – side).
Now, you are ready to complete the circuit. Touch the other end of the
battery (the + side) with the remaining wire. What happens? The electricity
flows through the light bulb causing its filament to glow, then out to
the other end of the battery.
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Humans
are not the only species that work with electricity. There are a number
of fish that can generate their own electric current. Most notable
is the electric eel. This swimming dynamo can generate 350 to 650
volts of electricity for about 1/500th of a second (your house uses
110 volts). In ancient times, physicians would treat patients' headaches
by dunking them in a tank of electric eels! After such a treatment,
clearly the headache would be the last thing on the patient's mind. |
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Note the brightness of the bulb, then try the same experiment with two
batteries joined together with tape. Now, how bright is the bulb?
A short circuit
results when the electricity finds a path with little resistance, so very
large current can flow. This may lead to wires getting so hot they can
burn and cause a fire. To prevent this, buildings have fuses that break
the flow of electricity should a problem with the electricity occur. Modern
fuses consist of circuit breakersswitches that automatically click off
when a dangerously high current is sensed. But many older buildings still
use wire fuses should a short circuit or overload on the wires occur.
A wire fuse consists of a thin piece of metal or wire contained in a glass
chamber. This metal breaks when an overload occurs and the fuse has to
be replaced. Try and create your own fuse in your circuit with a strand
of steel wool. Splice a small strand of the material in the wire that
connects the negative side of the battery with the light bulb (you can
use electrical tape to secure the wire). Now, touch the other wire to
the batteries. If there is enough current coming from your batteries,
the steel wool filament should quickly melt and break the circuit.
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