Download Lesson 4 Video Lesson

Lesson 4: Voltage
Part 1: Electric Potential Energy
Gravitational fields
Gravitational Potential Energy
A change in potential energy is called work.
When you increase the gravitational potential energy of a massive object, you should feel like you are
exerting a force against the gravitational field. This means moving the mass in the direction opposite to
the way it wants to go.
You don’t need to exert a force to decrease the gravitational potential energy of a massive object. If you
release a mass in a gravitational field, it should immediately start to move so that its gravitational
potential energy decreases.
Increase Gravitational Potential Energy
Electric fields
Decrease Gravitational Potential Energy
Electric Potential Energy
When you increase the electrical potential energy of a charged object, you should feel like you are
exerting a force against the electric field. This means moving the charge in the direction opposite to the
way it wants to go.
Positive charge
Negative charge
You don’t need to exert a force to decrease the electric potential energy of a massive object. If you
release a charge in an electric field, it should immediately start to move so that its electric potential
energy decreases.
Positive charge
Negative charge
Part 2: Voltage
Voltage is a concept closely associated with electric potential energy. Voltage is sometimes called
“electric potential difference” or even shortened to “electric potential” or “potential difference”
Voltage is:
Symbol:
Unit:
Formula:
Example: If 5.0 µJ of energy is required to move a 1.0 µC charge in an electric field, then the potential
difference between the two points is?
Example: A proton increases speed from 1.0 m/s to 4.0 m/s in an electric field. Through what voltage
did it move?
Example: An alpha particle is placed in an electric field with a potential difference of 100 V. If the alpha
particle is released within the field, what is the maximum speed that the alpha particle could attain?
Energy vs. Electric field warning!
The electron volt is a new unit of energy. It is the amount of energy an electron would gain in 1V
potential difference.
An electron volt is very small. We will use the eV instead of J when dealing with very small amounts of
energy.