This document summarizes key concepts about quantifying electricity including electric potential energy, electric potential difference (voltage), and how to calculate energy using voltage and charge. It defines electric potential energy as the amount of energy stored in each coulomb, measured in joules. It explains that voltage is the difference in electric potential energy on either side of a source or load, measured in volts. It provides an analogy that voltage is like the height of a waterfall, with higher voltage meaning more energy. Finally, it gives the formula that potential difference equals energy divided by charge, and provides an example calculation of energy used by a hair dryer.

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