Electric potential energy and gravitational potential energy both increase as work is done to overcome a field and raise an object or charge. Voltage measures electric potential energy per unit charge and represents how much energy a charge will gain or lose when moving through a potential difference. It is defined as the change in electric potential energy divided by the charge and can be measured in joules per coulomb (volts).

2. Electric vs. Gravitational Gravitational Electric
Potential Potential
Energy E Energy
g
Increases Increases
-
+
• Work is needed to
push an object • Work is needed to
against gravity and push a charge
give it Potential against a field and
Energy (PEg) give it Ele c tric
Po te ntia l Ene rg y

3. Allesandro Volta
Uniform Electric Fields
(Italian: 1745 – 1827)
Parallel Plates
Point
charge
Note the field lines
Uniform electric field

4. Low
Potential
Potential Difference
Potential Energy &
Energy
+++++++++ Low
2– – Potential
E Energy
High
Potential
--------- Energy
Higher Why does this one
Potential have more potential
Energy energy?

5. High or
Potential Difference
Potential Energy &
Low PE?
+++++++++
E 2+
---------
High or A change in
Low PE? PE means …

6. Potential ΔElectric Potential Energy
Difference = Charge of particle (C)
(J)
(V)
Potential Energy &
Potential Difference Voltage (scalar or vector)
What does voltage actually measure?
– Measures how much energy a charge
will gain/lose
– Measures how much work that can be
done by a charge
ΔPEelectric
ΔV = q
ΔV = = kQ
r

7. +++++++++
E
Potential Energy &
2–
–
---------
Which of these has
greater electrical potential
energy per charge?
Same ELECTRIC POTENTIAL
more ELECTRIC POTENTIAL
ENERGY

8. Battery gives the
electron 12 J of
Potential energy
e “loses” energy as it
travels through the
circuit.
Analogy
12 V
0V
Battery “gives” energy back
to electron to repeat cycle

9. Four ways to refer to voltage:
1. Electric Potential; units: V
2. Electric Potential Difference; units: V
3. Potential Difference; units: V
4. Voltage; units: V
If the word energy is included then the term
refers to electric potential ENERGY and the
units are Joules.

10. Electric Electric Electric
Potential Potential, Potential
Potential,
Energy Difference
Voltage
Defin- Total Energy per Change in
Key Ideas
ition Potential charge voltage
Energy
Unit Joules Volts (V) Volts (V)
(J/C) (J/C)
Equation PEe= kQq/r V = PE/q ΔV = ΔPE/q
= qEd
= qV

11. W = Fd F = kQq/r2
W = (kQq/r2)r
Hidden Equations
W = kQq/r = PEelectric
if PEelectric = W = qV  V = kQ/r
V = Ed
d and r for distance,
V for Voltage, W for Work, Q
and q for Charge, PE for