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 electric potential = energy (joules J)

Q 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

Formula

Current I amps A I = Q / T

Time T seconds S t = Q / I

Charge Q coulomb c Q = I x t

OR Q = E / V

Electric Potential

V volts V V = E / Q

Energy E joules J E = V x Q

OR E = P x t

Power P watts W P = E / t