FIGURE 20-12
-Two point charges of magnitude +4.00 μC and -4.00 μC are placed as shown in Figure 20-12. An additional charge of magnitude +2.00 μC is placed at point A. What is the electric potential energy of this system of charges?

Question

FIGURE 20-12 
-Two point charges of magnitude +4.00 μC and -4.00 μC are placed as shown in Figure 20-12. An additional charge of magnitude +2.00 μC is placed at point A. What is the electric potential energy of this system of charges?

Quizplus · Accepted Answer

The electric potential energy of a system of charges is given by EPE = kq1q2/r12 + kq1q3/r13 + kq2q3/r23, where k is the Coulomb constant, q1, q2, and q3 are the charges, and r12, r13, and r23 are the distances between the charges. Plugging in the values, we get:

EPE = (9 x 10^9 Nm^2/C^2)(4 x 10^-6 C)(-4 x 10^-6 C)/0.10 m + (9 x 10^9 Nm^2/C^2)(4 x 10^-6 C)(2 x 10^-6 C)/0.20 m + (9 x 10^9 Nm^2/C^2)(-4 x 10^-6 C)(2 x 10^-6 C)/0.30 m

Simplifying, we get:

EPE = -264 x 10^-3 J

The negative sign indicates that the system is bound, meaning it takes work to separate the charges.

FIGURE 20-12 -Two Point Charges of Magnitude +4.00 μC and -4.00 μC