Voltage – Electrical Potential
Voltage – or electric potential, is the
energy each electron has as it moves
through a circuit. The symbol for electric
potential is V and the units are volts (V).
• In order to measure the electric potential we
need to determine how much energy
(Joules) each coulomb has (6.0 x 1018
electrons).
V=E
Q
electric potential = energy (joules J)
charge (coulombs C)
Example A
• If a battery uses 45J of energy with a
charge of 15C what is the electric potential
of the battery?
V = E / Q = 45J / 15C = 3 V
Example B
• How many joules of energy are released
from a 9V battery that has a charge of
25C?
E = V x Q = 9 V x 25C = 225 Joules
Practice Problems:
1. What is the potential difference in a
battery if the charge is 45 C and 155 J of
energy are used?
V = E / Q = 150 J / 245 C = 3.4 V
2. If a 9 V battery has a charge of 46 C how
much chemical energy does the battery
have?
E = V x Q = 9 V x 46C = 414 Joules
3. What is the charge of a battery if it is 9 V
and has 600 J or energy?
Q = E / V = 600 J / 9 V = 66.6 C
4. How many joules of energy are released
from a 6V battery that has a charge of 250
C?
E = V x Q = 6 V x 250 C = 1500 Joules
5. If a battery uses 85 J of energy with a
charge of 25C what is the electric potential
of the battery?
V = E / Q = 85 J / 25 C = 3.4 V
Symbol Units
Unit
Symbol
A
Formula
I=Q/T
Current
I
amps
Time
T
seconds S
t=Q/I
Charge
Q
coulomb c
Q=Ixt
OR Q = E / V
V=E/Q
Electric V
Potential
Energy E
volts
V
joules
J
Power
watts
W
P
E=VxQ
OR E = P x t
P=E/t