Question

Two point charges, Q1 = 2.9 μC and Q2 = -1.3 μC , are placed on the x axis. Suppose that Q2 is placed at the origin, and Q1 is placed at the coordinate x1 = − 4.0 cm (Figure 1).

Part A

Part complete

At what point(s) along the x axis is the electric field zero? Determine the x-coordinate(s) of the point(s).

Express your answer using two significant figures. If there is more than one answer, enter your answers in ascending order separated by commas.

xE x E =

8.2

cm

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Completed

Part B

At what point(s) along the x axis is the potential zero? Determine the x-coordinate(s) of the point(s).

Express your answer using two significant figures. If there is more than one answer, enter your answers in ascending order separated by commas.

Answer 1

a)

there is only one point on the axis where net electric field is zero

let us consider that point is at a distance d to the right of q2.

now, at that point electric field due to each charge must be same

k q1 / ( 4 + d) ^2 = k q2 / d^2

4/d + 1 = sqrt ( q1/ q2)

4/d + 1= sqrt ( 2.9/ 1.3)

d = 8.1 cm

========

b)

there are two points where net potential considered to be zero

==>> between the charges

let us consider that the net potential is zero at a distance d to the left of q2

then

k q1 / (4 - d) = k q2 / d

4/d - 1 = 2.9 / 1.3

d = 1.238 cm

x co ordinate = - 1.238 cm

====>> to the right of q2

k q1 / (4 + d) = k q2 / d

4/d + 1 = 2.9/ 1.3

d = 3.25 cm

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