Name _______________________________________________
Date ____________
Electric Potential
We have spent some time talking about the Electrostatic force that exists between two
charged particles, and how it is that this force relates to the Electric Field. It is not
difficult to show that the farther apart the two charges are, the weaker the force becomes.
However, in order to move the charges apart, some amount of work must be done on the
particles.
The work done on the charges is converted to electrical potential energy. This is a very
similar concept to gravity. As you do work on an object to lift it (i.e., separate it from the
earth) that work is converted to gravitational potential energy.
The amount of PEg that something has is determined by two factors: the height, and the
mass. If two different objects are lifted to the same height h, then the mass is the variable
that will determine how much PEg an object will have.
We can define a term known as the gravitational potential, a quantity that will give us
the amount of PEg an object has with respect to its mass. This gravitational potential
would be equal to the gravitational potential energy divided by mass. In other words,
Gravitational Potential = Mgh
M
or
Gravitational Potential = gh
Gravitational Potential is in essence the amount of gravitational potential energy per unit
mass that any massive object will have. The gravitational potential is determined solely
by the physical environment and is not dependent on the individual mass. This indicates
that, for a given height, we can determine the amount of potential energy that any mass
will have. There is a similar concept in the field of electrostatics. When two charges are
separated from one another, there is a certain amount of electrical potential energy
inherent to the system.
We can define a term known as Electric Potential (V) as the amount of electrical
potential energy a certain charge has divided by that charge. In other words,
Electric Potential = Electric Potential Energy
Charge
or
V = PEE
Q
Electric Potential
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Bradshaw 04-05
Name _______________________________________________
Date ____________
Please consult the following visual aid:
The picture on the left shows two different masses elevated to the same height h. The
two objects have different masses, and hence they have different values of PE g; however,
they have an identical amount of gravitational potential.
The picture on the right shows two different charges (q and 2q) that are placed in an
identical electric field. They have different amounts of electrical potential energy, but
they have the same Electric Potential.
[Note: this is a picture that represents what is known as a Parallel Plate Capacitor, an
electrical device that stores electric charge. The Electric Potential for a parallel plate
capacitor is defined as the Electric Field between the plates times the distance between
them. We will speak about Capacitors in detail in the future.]
Electric Potential is measured in units called Volts (V). Electric Potential is often
referred to by other names. It is simply called Potential, and is commonly referred to as
Voltage. We will use these terms interchangeably in class.
We will deal with V in two distinct ways:
1. Parallel Plate Capacitor – As shown above, V = Ed where d is the distance
between the plates.
2. Potential due to a single charge – Much like electric fields, there is a certain
Potential due to the presence of an electric charge. To find the Potential V a
distance r from a charge q:
V = kq
r
Electric Potential
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Bradshaw 04-05