19. Three 1.0 μC charges are placed along the x-axis, one charge at x = -10 cm, another at the origin, and the last one at x = 10 cm. What is the total potential energy of this arrangement?
A. 0.27 J
B. -0.27 J
C. 0.72 J
D. 0.23 J
E. infinite (or indeterminate)
20. Three point charges, q1 = 2.0 μC, q2 = 2.0 μC, and q3 = -1.0 μC, are located at the vertices of an equilateral triangle of side length 30 cm. What is the potential energy of this arrangement?
A. 0.24 J
B. 0.12 J
C. -0.24 J
D. -0.12 J
E. 0
21. Three point charges, q1, q2, and q3, are located at the vertices of an equilateral triangle. If q1 = q2, what value must q3 have so that the total potential energy of the arrangement is zero?
A. q1
B. 0.5 q1
C. -0.5 q1
D. (q1 + q2)/2
E. no value will have this result