18.2) Two point charges are fixed in placed on an x axis. Particle 1 of charge q

Question

18.2) Two point charges are fixed in placed on an x axis. Particle 1 of charge q1 = q is located at x = 0, while particle 2 of charge q2 = -q/2 is located at x = +d. Consider a point P located on the x axis at x = (2/3)d. Let q = 8 nC and d = 0.03 m.

a)What is the direction of the electric field at point P?

b)What is the magnitude of the electric field at point P?

c) A 1-nC charge is placed at point P and then released from rest. What is the electric force on this charge immediately after it is released?

Explanation / Answer

Given ; particle 1 has charge q = 8 nC and positioned at (0,0)

particle 2 has charge -q/2 = -4 nC and placed at (d,0) = (0.03,0)

point P is located at (2/3 d ,0 ) = (0.02 , 0 )

a) particle 1 has electric field that points in +ve x- direction

particle 2 also has electric field that points in +ve x- direction

so the net electric field at point P points in the +ve x- direction

b) magnitude of electric field

Enet = E1 +E2

Enet = kq1/r1^2 + kq2/r2^2

Enet = 9*10^9 * ( 8*10^-9 / 0.02^2 + 4*10^-9/0.01^2)

Enet = 540000 N/C

c) a 1nC charge is placed at point P

electric force = charge * electric field

F = qE

F = 1*10^-9*540000

F = 5.4*10^-4 N

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