Hey it's professor, Dave let's learn
about electric potential.
We now know about the electric force and the
electric fields that propagate this
force, so how is this useful to humans?
To answer this we must understand that just
as there is gravitational potential
energy by virtue of an object's position
in a gravitational field, there is also
electrical potential energy by virtue of
an object's position in an electric
field, and charged particles can flow and
generate current just like water in a
river can flow and generate its own kind
of current. Oppositely charged particles
because of their charge have the
potential to accelerate towards each
other, just like an object on the edge of
a cliff has the potential to accelerate
towards the earth because of its mass,
and in each case it is the field that
does the work to produce the
acceleration. As charged particles move
within an electric field their
electrical potential energy changes. For
a uniform field the magnitude of this
change is equal to the opposite of the
object's charge times the electric field
strength times its displacement from the
reference point in the direction of the
field. This leads to the concept of
potential difference, which is the
difference in electric potential between
two points in an electric field
expressed as the change in electrical
potential energy over electrical charge.
The SI unit for potential difference is the
volt, which is equivalent to one Joule
per Coulomb. This means that as a one
Coulomb charge moves through a potential
difference of one volt it gains one
Joule of energy. The potential difference
for the two terminals of a common
battery is anywhere from about 1.5 volts
for small batteries to around 12 for a
car battery. Batteries do work to move
charges, so volts are not a measure of
energy, they are a measure of change in energy
per unit charge. As charge flows it
produces usable energy, like the way that
flowing water can push a waterwheel as
it moves past. In this way we can discuss
electric current, and our ability to
manipulate this current is responsible
for our mastery of electrical power.
A current exists whenever there is a net
movement of electric charge through a
medium. This can be defined as the total
charge passing through a given area
divided by the time interval. The SI unit
for current is the ampere, which is
equal to one Coulomb of charge passing a
particular cross-sectional area per
second. The direction of the current is
always opposite the movement of negative
charges, but a current can be generated
by particles of either charge.
Most materials that are conductors of
electricity are metals that allow for
the free movement of electrons from atom
to atom, or electrolytic solutions with
charged ions in solution. The ability of
a material to oppose the motion of
charge is called resistance, which will
be unique to a substance and vary by the
dimensions of the material. This is the
ratio of potential difference to current
measured in ohms, which are represented
by the Greek letter Omega. These are
equal to 1 volt per ampere. Electric
power, which is the rate at which charge
carriers convert electrical potential
energy to other forms of energy, is given
by current times potential difference
which is measured in watts, or joules per
second. An incredible amount of
technology has been developed to utilize
all these phenomena in the form of
circuitry, particularly in computing
which becomes more sophisticated every
year, but an in-depth analysis of
circuits will have to wait for an
engineering course sometime in the
future. For now, let's quickly list a
summary of the new units we have just
defined, as they can get a little
confusing. With all of that in order
let's check comprehension.
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