Question

Chapter 18, Problem 48 GO The drawing shows a positive point charge +q1, a second point charge q2 that may be positive or negative, and a spot labeled P, all on the same straight line. The distance d between the two charges is the same as the distance between q1 and the spot P. With q2 present, the magnitude of the net electric field at P is twice what it is when q1 is present alone. Given that q1 = +0.201 determine the magnitude lq2l when q2 is (a) positive 92l and (b) negative. 42l 92

Answer 1

electric field in absence of q2

E = k q1 / d^2

E = k* q1 / d^2

a)

Considering q2 to be positive

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

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

q1 / d^2 = = q2 / 4 d^2

q2 = 4 q1

q2 = 0.8 uC

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b)

Considering q2 to be negative

2 k q1 / d^2 = k ( q2 / (2d)^2 - q1 / d^2)

3 q1 / d^2 = q2 / 4 d^2

q2 = 12 q1

q2 = 2.4 u C

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