Chapter 21, Problem 21.14E

In Example 21.4, suppose the point charge on the y-axis at y = −0.30 m has negative charge −2.0μC, and the other charges remain the same. Find the magnitude and direction of the net force on Q. How does your answer differ from that in Example 21.4? Explain the differences.

Example 21.4     VECTOR ADDITION OF ELECTRIC FORCES

Two equal positive charges q₁ – q₂ – 2.0 μC are located at x = 0, y = 0.30 m and x = 0, y = −0.30 m. respectively. What are the magnitude and direction of the total electric force that q₁ and q₂ exert on a third charge Q = 4.0 μC at x = 0.40 m, y = 0?

SOLUTION

IDENTIFY and SET UP: As in Example 21.3, we must compute the force that each charge exerts on Q and then find the vector sum of those forces. Figure 21.14 shows the situation. Since the three charges do not all lie on a line, the best way to calculate the forces is to use components.

Figure 21.14 Our sketch for this problem.