A ring-shaped conductor with radius a = 2.10 cm has a total positive charge Q =
ID: 1522952 • Letter: A
Question
A ring-shaped conductor with radius a = 2.10 cm has a total positive charge Q = +0.125 nC uniformly distributed around it, as shown in the figure below. The center of the ring is at the origin of coordinates O.
(a) What is the electric field (magnitude and direction) at point P, which is on the x-axis at x = 60.0 cm? Answer in N/C
(b) A point charge q = -2.00 µC is placed at the point P described in part (a). What are the magnitude and direction of the force exerted by the charge q on the ring? Answer in N
Explanation / Answer
given
Q = +0.125 nC = 0.125*10^-9 C
a = 2.1 cm = 0.021 m
a) at x = 60 cm = 0.6 m
Electric field n the axis of the ring,
E = k*Q*x^2/(x^2 + a^2)^(3/2)
= 9*10^9*0.125*10^-9*0.6^2/(0.6^2 + 0.021^2)^(3/2)
= 1.87 N/c
b) Force exerted by the charge q on the ring,
F = q*E
= 2*10^-6*1.87
= 3.74*10^-6 N
direction : towards +x axis
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