60 June 2014
with fewer electrons (hey, that’s what quantum physicists
say if you read between the lines). Areas with more
electrons are said to have a higher electric potential relative
to areas with fewer electrons. Figure 1 shows this with
holes at different depths along the side of a bucket. This
potential difference (more electrons in one area and less in
another) can be thought of as a force that pushes electrons
from one place to another. Voltage is a measure of the
electric potential difference between two areas that have
different amounts of electrons. Water will run down hill if it
can run down hill, and electrons will spread out from higher
electron density regions to lower electron density regions if
they can spread out.
Electric Current = Amps
We think of current as the amount of water moving
past in a stream. The Gulf Stream, for example, has a lot
more water moving along than what comes out of your
bathroom faucet. A bolt of lightning has a lot more
electrons moving past than the spark of static electricity
your older brother applies to your ear after sliding his
bunny slippers across the wool carpet in the hall on a dry
day. The amount of electric current is referred to as
amperes or amps. Figure 2 uses the water bucket metaphor
with larger holes allowing greater current. Pressure is the
same, but as the holes get bigger you get a greater current.
Electric Resistance = Ohm (Ω)
For the water analogy, we can think of resistance as
being caused by the diameter of the hole. Note that in
Figure 2 more current is due to different size holes —
bigger hole, less resistance, more water.
For the resistors in the projects kit (available at the NV
Webstore), the higher the number, the more the resistance.
So, you can think about the 10K Ω resistors as having a
smaller electric hole and thus passing less current than
1K Ω resistors which have a bigger hole and pass more
current. Materials with low resistance are known as
conductors, while materials with high resistance are known
as insulators. Electrons move easily in some things such as
copper wire (a good conductor), but are stopped cold by
some things such as glass (a good insulator). Copper has
very low resistance — jumper wires can have near zero
ohms of resistance (about one ohm per 62 feet), while
glass can have millions of ohms of resistance.
Georg Simon Ohm wrote a rule to account for
observations of voltage (volts), current (amps), and
resistance (ohms). We typically see this rule as voltage is
equal to current times resistance:
Volts = Amps Ohms
Voltage equals current times resistance.
A little algebra shows us that the equivalents are:
Amps = Volts/Ohms
Current equals voltage divided by resistance.
Ohms = Volts/Amps
Resistance equals voltage divided by current.
Now, let’s confuse things a little bit and use the
standard (SI) symbols for this:
V = IR Voltage equals current times resistance.
The confusion is that ‘I’ is the symbol for amps. This is
what is used, so let’s just go with it:
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■ FIGURE 1: Bucket
■ FIGURE 2: Bucket current metaphor.