American Cinematographer - January 2019 - 22

Deep Focus
The Basics of
Electromotive Force

22

To understand how electricity
works, we need to break it down into its
most simplistic form. This requires a journey back in time to high-school science
class, where we'll revisit atomic theory.
Don't worry, we won't stay there long.
Hydrogen has the simplest atomic
structure of all of the elements on the
periodic table. The hydrogen atom has a
nucleus, with one proton at its center and
one electron orbiting around it. If you'll
remember from yesteryear's science class,
the number of protons, which are positively charged, is always equal to the
number of electrons, which are negatively
charged, in atoms that are electrically
neutral.
However, when you have one lone
electron out in its own orbit - as is the
case with the hydrogen atom - it can
become easily dislodged. This, in turn,
changes the polarity of the atom from
neutral to positive. Atoms, as it turns out,
don't like to be imbalanced, so this little
atom will now steal the electron from a
neighboring atom to make itself neutral
once again. This kicks off a chain reaction
of moving electrons right on down the
line, from atom to atom - and this
exchange of electrons is called electromotive force.
All conductors, which are materials
January 2019

that allow for the easy flow of electric
current, have this free electron in the orbit
of their individual atoms.The best conductors are metals: silver, gold, copper and
aluminum (in that order, with silver being
the most conductive).
Copper is one of the most
common conductors used, as it offers the
best balance of conductivity to cost -
although aluminum was used quite heavily
in the 1970s and '80s, and in some cases
can still be found. If we look at the atomic
structure of copper, we'll see that it has 29
electrons and 29 protons, but the 29th
electron is in its own orbit and is therefore easily dislodged.
It's important to remember that
heat is a byproduct of electromotive force
- the transfer of electrons generates
heat. And in high enough amounts, of
course, heat can cause fire. Mishandled, the
flow of electrons through a conductor can
easily cause materials around the conductor to melt or burst into flames.This makes
fire one of the greatest hazards in electricity (alongside electrocution).
In a previous Shot Craft ("Keeping
the Lights On," AC March '18), we looked
at three of the principal elements of electricity: volts, amps and watts. Let's take
another look at those, along with a fourth:
ohms.
If you think about the flow of electricity like the flow of water, some of these
components are easier to understand.
Imagine a large bucket of water with a
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When a lone electron
is in its own orbit -
as is the case with both
the hydrogen and copper
atoms - it can be easily
dislodged, setting off a chain
reaction of moving electrons
called electromotive force.

spigot at the bottom. If the bucket is resting on the ground and you open the
spigot, water will spill out onto the ground
at a certain pressure. If you raise this
bucket up into the air, though, and then
attach a pipe to the spigot, the water pressure at the ground level is going to be
greater than it was when the bucket was
on the ground.
In the most simplistic terms, this is
the same principle as voltage, which is the
measurement of the electrical potential
between two points, or the measurement
of how many free electrons are available
to pass from point A to point B. In other
words, voltage - which, remember, is also
known as electromotive force, and therefore is often abbreviated with the letter E
in mathematical equations - is the
measurement of the "pressure" of electrical flow.
Amperage - which is also
referred to as "intensity" and is often
abbreviated with an I in mathematical
equations - is the measurement of the
capacity of flow of electrons. How many
electrons are flowing past a given point at
a given time? Amperage is dictated by the
capacity of the conductor and is directly
related to the amount of electricity ultimately produced.
If you think about amperage as the
diameter of the pipe connected to the
bucket, it's easier to grasp the concept. If
you have a 1⁄ 2"-diameter pipe attached to
the bucket, no matter how much pressure
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