Charge q 1 = 9.5 nC is located at the coordinate system origin, while charge q 2
ID: 1404317 • Letter: C
Question
Charge q1 = 9.5 nC is located at the coordinate system origin, while charge q2 = 3.7 nC is located at (a, 0), where a = 0.55 m. The point P has coordinates (a, b), where b = 0.4 m. A third charge q3 = -9.5 nC will be placed later. Find the electric potential VP at point P, in volts. Assume the potential is zero at infinity. How much work W, in joules, would you have to do to bring the third charge, q3, from very far away to the point P? What is the total potential energy U, in joules, of the final configuration of three charges?
Explanation / Answer
electric potential Vp at point P = K q1 /r1 + kq2/r2
Where q1 and q2 are charges
r1 and r2 is distance between charge q1 ,q2 and point respectively.
k = 8.99 x 109 N m2/C2
r1 = sqrt(0.552 + 0.42)
r1 = 0.68m
r2 = sqrt(0.42)
r2 = 0.4m
Vp = k (q1/r1 + q2/r2)
Vp = 8.99 x 109 N m2/C2 (9.5*10^-9 / 0.68 + 3.7 * 10^-6 / 0.4 )
Vp = 8.33 * 10^4
Elecric Potential at point p is Vp = 8.33 * 10^4
We know , work is the same as q times the absolute potential at point.
W = q3 * Vp
W = 9.5 * 10^-9 * 8.33 * 10^4
W =7.9 * 10^-4 J
Work done to bring third charge from far away to point p is W =7.9 * 10^-4 J