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Practice Problems — Calculating Electric Potential Energy (Continued) 3. How far apart are two electrons if the potential energy to bring one of the electrons from infinity is 9.45 × 10–20 J?
In summary, when two charged objects interact, we can explain the interaction by describing the forces on each object in the system using Coulomb’s law (see section 5.2) or we can describe the potential energy associated with the interaction. Electric potential energy depends on the amount of electric charge and the distance from the source charge. When two charges are separated by a distance, the electric potential energy associated with the interaction is:
Summary
Ep = k
Q1Q2 r
We define infinity as the point at which the potential energy for one charge is zero.
Quick Check For each of the following situations, explain what will happen to the potential energy in the test charge. 1. A positive test charge is moved from A to B. B
E
A
2. A positive test charge is moved from B to A. B
E
A
3. A positive test charge is moved from A to B. E
B
A
4. A positive test charge if moved from B to A. E
B
186 Chapter 6 Electrostatics
A
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