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Electrical Potential
Voltage
How can we manipulate energy
in electric fields?
Apply FORCE to push like charges TOGETHER
FA
+
+
FA
Apply FORCE to push unlike charges APART
+
FA FA
-
Electric Fields
•The electric field can store energy.
Charges gain potential energy when moved against the
field in the same way as masses gain energy when lifted
against gravity.
•The electric field can do work! (remember the
work/energy connection) when they move charges.
Work done against the field to move the charge
equals PE or KE gained by the charge
Electrical Potential Energy
a.
In an elevated position, the ram has gravitational potential energy.
When released, this energy is transferred to the pile below.
Electrical Potential Energy
a.
In an elevated position, the ram has gravitational potential energy.
When released, this energy is transferred to the pile below.
b.
Similar energy transfer occurs for electric charges.
Electrical Potential Energy
• The energy a charge has due to its
location in an electric field is called
electrical potential energy.
Electric Potential
• If we push a single charge against an electric field,
we do a certain amount of work.
• If we push two charges against the same field, we do
twice as much work.
• Two charges in the same location in an electric field
will have twice the electrical potential energy as one;
ten charges will have ten times the potential energy.
• It is convenient when working with electricity to
consider the electrical potential energy per charge.
Electric Potential
The electrical potential energy per charge is the total electrical
potential energy divided by the amount of charge.
At any location, the potential energy per charge—whatever
the amount of charge—will be the same.
The concept of electrical potential energy per charge has
the name, electric potential.
Electrical Potential
• Electrical Potential is also called VOLTAGE or
ELECTRICAL POTENIAL DIFFERENCE, or
POTENTIAL DIFFERENCE
• Unit for electrical potential  VOLT
• 1 Volt = 1 Joule/Coulomb
W
V
q
1V = 1 J/C
Amount of work done in moving a charge
and
the amount of charge moved
Example #1
6.0 joules of work are done pushing an object with
3.0 coulombs of charge toward a charged plate.
• How much electrical potential energy was stored in the electric
fields?
6.0 J
• What is the electrical potential difference in the field between
the charged object and the plate?
V = W/q
V = 6.0 J / 3.0 C
V = 2.0 V
Example #2
Removing Energy
An object with 2 coulombs of charge
• This
stored energy
can also
be released.
is accelerated
using
an electrical
potential difference of 10 volts.
• What happens to energy The
thatfield
comes
OUT
releases
How
much kinetic energy
doesdoing
the
of
a field?
the energy,
receive?
WORK on the charge!
– Transfers object
into kinetic
energy
V=W
q
STORING
W =ENERGY
qV
W = (2C)(10 V)
- -W =- 20-J - -
-
-
-
-
-
-
Example #3
• An object with a charge of -0.5 coulombs is
pushed 0.2 meters toward a negatively charged
plate with a force of 10 newtons.
• What is the energy required to do this?
W = Fd = (10 N)(0.2 m) = 2 J
• What is the potential difference between the
object and the plate after it is pushed?
V= W = 2J =4V
q
0.5 C
Example #4
An electron is raised through a potential
difference of 3000 volts.
What is the work done on the electron?
V= W/q
W = Vq = (3000 V)(1.6 x 10-19 C) = 4.8 x 10-16 J
Electron-volts
The electron-volt (eV) is an alternate unit of ENERGY.
Electron-volts are a SHORT CUT to finding
ENERGY when dealing with
ELEMENTARY CHARGES.
An electron-volt
is
the
amount
ofto
energy
What
is the
energy
What
is the
energy
needed
needed
toelectrons
raiseto
1 elementary
charge
neededraise
to raise
a potential
ofvolts?
1 volt?
two two
electrons
a to
potential
of
2.5
through a potential difference of 1 volt.
W = 2e
W=qV
1V
2.5V
W x Vq
V
q==25eV
eV
19
19
-19 J
2
eV
=
3.2
x
10
W  (1V )(15.6 x10 8.0
C )  1.6 x10 J  1eV
Higher VOLTAGE
What use is electrical potential?
We use this by putting a
RESISTOR
in the
The
A battery
electrons
is a naturally
tool
thatpath
forces
“want”
the ELECTRONS
– as
toofelectrons
drop
to a lower
to a higher
energy
they goP.E.
through
electrical
- gives
the them
RESISTANCE
they
How
do they
VOLTAGE
get there?
do WORK on it!
RESISTOR