Electrostatics 2 Question 5

5. Three charges Q,+q and +q are placed at the vertices of a right angle isosceles triangle as shown below. The net electrostatic energy of the configuration is zero, if the value of Q is (Main 2019, 11 Jan I)

(a) 2q

(b) q1+2

(c) +q

(d) 2q2+1

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Answer:

Correct Answer: 5. (a)

Solution:

  1. Electrostatic energy between two charges q1 and q2 such that the distance between them r is given as

U=Kq1q2r

In accordance to the principle of superposition, total energy of the charge system as shown in the figure below is

U=Kq2a+KQqa+KQq2a

It is given that, U=0

Kqaq+Q+Q2=0

Q=2×q(2+1)



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