The next property of electricity we need to explore is called voltage. A volt is
another one of those quantities that has been given a name from someone in
history who contributed a significant finding to the field of physics. In this
case, Alessandro Volta from northern Italy who in 1775, may have developed the
first practical battery. At least, he was the first to publish his findings
after he constructed it while it is believed that possibly the Phoenicians or
Greeks may have discovered the properties of a battery much earlier in history.
Since they didn’t publish their findings, they didn’t get the credit. The first
electrical device Volta adapted and publicized in 1775 was quite simple. Two
circular metal plates perhaps six to eight inches in diameter and a quarter inch
thick were assembled. The top plate was fitted with a wooden handle and the
lower plate was coated with wax or pitch. The wax acted as an insulator. The top
plate was briskly rubbed with fur to create a static electric field on the plate
which could then be transferred to other devices by holding the plate with the
insulated wooden handle and touching the plate to something. Placed on the wax
covered plate, the charge would migrate into two parts, a negative charge on the
top of the plate and a positive charge on the bottom of the plate. Both would
remain for long periods of time until discharged by touching to ground and
bleeding off the held charge. Volta called the device an electrophorus but
today, we know it as a capacitor, not really a battery but more a charge storage
device. We’ll talk more about capacitors, a basic electronic device, a bit
later.

The battery came about in 1800 while Volta was disagreeing with his contemporary
colleague, Luigi Galvani, a doctor and anatomy instructor. Galvani had reported
that he was able to cause a dead frog’s dissected legs to twitch by touching the
exposed sciatic nerve with a metal scalpel. Galvani suggested that the frog
muscles were activated by an electrical fluid carried by the nerves. Volta
asserted that the electrical stimulus was created externally to the frog. To
disprove Galvani’s animal electricity theory, Volta assembled plates of
dissimilar metals, silver and zinc, stacking them with separators soaked in salt
water (which he said worked better than plain water) and connecting them to the
frog’s nerve, he could make the legs twitch as well. The ability to create an
electric current without having to rub an object with animal fur was a
significant contribution and was termed the voltaic pile or cell.

Volta’s experiments with his pile revealed some characteristics that had not
previously been known. Increasing the size of the pile also increased the
magnitude of the electric charge it produced. Outside of noting that brine
soaking the separators between the plates produced more charge than plain water,
he did not experiment with other fluidic solutions, what we now call
electrolytes. He noted that different metals used for the plates produced
different charge values. Other investigators would explore the characteristics
of the voltaic pile in great detail and since it permitted drastically more
consistent investigation of electricity, most physicists used similar variations
of the concept as well.

As an interesting aside, Volta happened to read a paper written by Benjamin
Franklin that described a “flammable air” found hovering over lakes. That air
turned out to be methane, created by rotting vegetation at the bottom of lakes.
Volta isolated the gas in 1778 and collected it in vessels to study it from Lake
Maggiore, a large lake along the border of Italy and Switzerland.

By 1830, Michael Faraday noted that the chemical reaction of a salty or acidic
solution with metallic electrodes was the source of the electric current.
Faraday was able to describe the chemical reaction that caused electrons to
collect, or migrate, or flow from one of the electrodes to the other. It became
noted that if the electrodes were connected with a conductor, the electric
charge would flow from areas of higher charge to areas of lower charge. The
higher charged electrode was labeled as negative, the lower charged electrode
was labeled as positive. It was also noticed that the flow of charge did not
necessarily have to be from negative to positive, it just had to be from an area
of more intense charge to an area of less intense charge, or from a more
negatively charged point to a less negatively charged point or from a less
positive area to a more positive area.

Now that we know that electric charges can migrate or move from one point to
another via a conductor (there are many such as copper, silver, gold, aluminum,
and ionic fluids like brine). If we cause one ampere of charge to move through
that conductor in one second, we can say there is a charge potential difference
between the points connected by the conductor of one volt. Voltage then is the
cost in energy required to move a unit of charge. Or, stated differently, it is
the potential difference that will transfer one joule of energy per coulomb of
charge. Wait. Joule? Didn’t we see that in the description of current and the
amount of energy contained within the proton?

Indeed. The joule is a name given to the amount of work done by applying a force
of one newton through a distance of one meter. Or, passing one ampere of
electric current through a resistance of one ohm for one second, or an electric
charge of one coulomb through a potential difference of one volt, and finally
the work of one watt for one second. All these values of energy are equivalent,
just expressed differently using different units.

Voltage is a bit more difficult to explain than the basic electron charge and
the flow of charges, current. Voltage may be thought of as the pressure behind
the charge, pushing it harder and harder as the voltage increases. If there is
no pressure difference between two points, there is no current flow and there is
no voltage. Sometimes it will be necessary to measure a voltage at a point,
which may be a bit confusing to you right now because we just said there had to
be two points. Indeed, it is often assumed that the “second point” which has not
been identified, is a ground potential point. Ground is a neutral reference
point in electronics which permits voltages to be either positive or negative
with respect to that neutral ground.

The abbreviation “V” is used to refer to volts, and usually E or e in equations.
Also, mV for millivolt (1 thousandth of a volt) or uV for microvolt (1 millionth
of a volt).

Now that we have been introduced to the two most common characteristics of
electricity, current and voltage, we can introduce a third, resistance.

73… W3SEH