negatively charged portion of the balloon is
attracted to the wall.
Now tear up the paper into small pieces
and rub the balloon again. You can pick up
the small bits of paper with the charged
portion of the balloon. A strong enough
charge will actually cause the pieces of
paper to leap up to the balloon.
What About Circuits?
Electricity doesn’t do us much good unless
we can control it in order to do useful
work. Scientists learned to do this with
circuits. First, they discovered that a circuit
must be complete in order for the elec-
tricity to flow. Think of a circuit as a circle.
When the circuit is complete, electricity
can flow; we call that a “closed” circuit.
When there is a break anywhere in the
circuit, electricity cannot flow, and we call
that an “open” circuit. Second, electricity is
lazy. It will always follow the path of least
resistance.
Electric circuits are comprised of three
connected parts:
1. An energy source, such as a battery
2. A conductive path for the electricity
to flow through, such as a wire
3. A load that uses electricity to do
work, such as a light bulb
Try This at Home!
Here’s a simple circuits experiment you can
do with your children. All you need is a
battery (AA, C, or D will work), a small
piece of wire, and a flashlight bulb. If you
don’t have them at home, you can get the
wire and bulb from any hardware store, electronics store, or the science fair section of a
hobby shop. We used some surplus electric
fence wire we had at home and borrowed a
bulb and battery from a flashlight.
Connect the bulb to one side of the
battery as shown in Figure 1 (on the
following page). We’ve connected the bulb
to an energy source, so why doesn’t it light
up? It doesn’t light up because it’s an open
circuit: there’s no path on which the current
can get back to the other side of the battery
to complete the circuit. Now connect the
circuit as shown in Figure 2. The current
flows through the bulb back to the battery
and the bulb lights up. Congratulations,
you’ve just created a working circuit!
Now let’s modify that circuit to build an
insulator/conductor tester. You’ll need two
more wires. You may find it easier to use
jumper wires with alligator clips. (These
are small versions of the jumper cables for
your car and can be found in the same
shops mentioned above.)
