Concept #1: Electric Potential Energy

A point charge q1 = 4.00 nC is placed at the origin. A second point charge q 2 = -3.00 nC is placed on the x-axis at x = 20.0 cm. A third point charge q3 = 2.00 nC is placed on the x-axis between q1 and q2. Assume that the potential energy of the three charges is zero when they are infinitely far apart. Determine the electric potential energy of the system of the three charges if q3 is placed at x = 10.0 cm.

A system of charges are shown in the figure. What is the electric potential energy of the following system of charges?
1. U = kQ2 / ℓ
2. U = 0
3. U = kQ2 / 3ℓ
4. U = kQ2 / ℓ2
5. U = - kQ2 / 2ℓ
6. U = - kQ2 / ℓ
7. U = - kQ2 / 3ℓ
8. U = kQ2
9. None of these.
10. U = kQ2 / 2ℓ

Three point charges shown below are located at the vertices of an equilateral triangle. If the electric potential energy of two point charges is defined to be zero if the distance between them approaches infinity, the total electric potential energy of the system of those three charges is
A) Positive
B) Zero
C) Negative
D) All of the above

If a negative charge (-Q) is placed at point P in the above diagram, which situation minimizes the electric potential energy?A) Situation AB) Situation BC) Situation CD) Situation D

Three equal point charges, each with charge 1.35 μC, are placed at the vertices of an equilateral triangle whose sides are of length 0.250 m. What is the electric potential energy U of the system? (Take as zero the potential energy of the three charges when they are infinitely far apart.) Use ϵ0 = 8.85 x 10-12 C2/Nm2 for the permittivity of free space.