1. Quantifying Electricity:
Energy

2. Quantifying Electricity
Electric Potential Energy: The amount of energy stored
in each Coulomb. Energy is what operates a load.

3. Electric Potential Energy
Symbol for Energy: E
Unit of Measurement: Joule (J).

4. Charge
For example, if we say that it takes 2000 J to
heat-up a cup of water, then
E = 2000 J

5. Quantifying Electricity
Electric Potential Difference (Voltage): The difference
in the amount of energy Coulombs have on both sides
of a source or load.

6. Electric Potential Difference
In circuits we don't measure total energy. We measure
how much energy is gained or lost across loads or sources.

7. Potential Difference Analogy
The water at the top of the waterfall
has a lot of energy. The higher the
waterfall, the more energy the water
has.
At the bottom of the waterfall,
the water has less energy.
The voltage across part of an
electric circuit is like the distance
that the water falls.
The higher the voltage, the more
energy the current has.

8. Potential Difference Analogy
Which has greater potential difference?

9. Electric Potential Difference
A voltmeter is a device that is used
to measure voltage in a circuit.
Symbol for
voltmeter
Voltmeter

10. Electric Potential Difference
Symbol for Potential Difference: V
Unit of Measurement: Volt (V).

11. Charge
For example, if the potential difference
across a light bulb is 120 Volts, then
V = 120 V

12. Calculating Electric Potential Difference
Potential Difference = Energy
Charge
Volt = Joule
Coulomb
V = E
Q
Name Unit Symbol
Potential Difference Volt V
Energy Joule E
Charge Coulomb Q

13. Try This.
(Problem Set Voltage Question #1)
A hair dryer has 1.2 × 103 C of charge passing through a
point in its circuit when it is connected to a 120 V
power supply. How much energy does the hair dryer
use?
V = E
Q
E = VxQ
E = (120 V) x (1.2 x 103 C)
E = 1.4 x 105 J
.: the hair dryer uses 1.4 x 105 J of energy