# PHYS 2212 Module 3.1

## Electric Potential Energy

3.1 Electric Potential Energy

### Learning Objectives

By the end of this section, you will be able to:

• Define the work done by an electric force
• Define electric potential energy
• Apply work and potential energy in systems with electric charges

### Electric Potential Energy

Practice!

Discuss!

Reflect on these questions and take notes on how you would answer them. Then we will share these thoughts together in a class discussion.

At the instant shown, a positively charged particle is moving at 5 m/s in the direction of a uniform electric field. Someone makes the following statement: “As the particle continues to move in the direction of the electric field, the particle will gain potential energy since it is moving in the direction of increasing electric potential energy.”

What, if anything, is wrong with the above statement? If something is wrong, explain the error and how to correct it. If the statement is valid, explain why.

Is the electrical potential energy of two point charges positive or negative if the charges are of the same sign? Opposite signs? How does this relate to the work necessary to bring the charges into proximity from infinity?

A proton (mass m, charge +e) and an alpha particle (mass 4m, charge +2e) approach one another with the same initial speed v from an initially large distance. How close will these two particles get to one another before turning around?

(Your final answer will be in terms of k, e, m, and v.)