2. Electric vs. Gravitational Gravitational Electric
Potential Potential
Energy E Energy
g
Increases Increases
Potential Energy
-
+
• 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 Electric
Potential Energy

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?
+++++++++
2+
E
---------
High or A change in
Low PE? PE means …

6. Some stuff you should remember:
Potential Energy & W= ΔPE
W= F d
Fon test= q E
charge
Some new stuff
W= ΔPE
ΔPEelectric F dE d
W== q
Fon test= q E Only for uniform
charge electric field
Why?

7. Potential ΔElectric Potential Energy (J)
Difference = Charge of particle (C)
(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 = qEd = kQ d = kQ
r
q 2 r r
fyi: k = 1/(4πεo) εo=8.85 x 10-12 C2/Nm2

8. +++++++++
E
Potential Energy &
2–
–
---------
Which of these has
greater electrical potential
energy per charge?
Same ELECTRIC POTENTIAL
more ELECTRIC POTENTIAL
ENERGY

9. +++++++++
Potential Energy &
2– –
E
---------
WhichWhich of has experienced
of these these has
a greater change in electrical
experienced a greater
potential energy per charge?
change in electrical
potential energy?

10. 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

12. • Sample Problem
The electric field is 625 N/C between 2
Potential Energy &
large charged parallel plates are 4 cm
apart.
a. What is the electric potential difference
between the plates?
b. What work will you do to move a proton
from the – to the + plate?
+ + +
E = 625 N/C
D = 0.04m d = 0.04 m
– – p+ q = 1.6 x 10-19 C
–
a) V = E d b) W = PEe = q ∆V
= (625N/C)(0.04m) = (25 V)(1.6 x 10-19C)
= 25 V PEe = 4.0 x 10-18 J

13. 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 Volts
(J/C) (J/C)
Equation PEe= kQq/r V = PE/q ΔV = ΔPE/q
= qEd
= qV

14. W = Fd F = kQq/r2
W = kQq/r2 r
Hidden Equations
W = kQq/r = PEelectric
if PEelectric = W = qV  V = kQ/r
k = 1/(4πεo)
εo=8.85 x 10-12 C2/Nm2