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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 : Q +q +q

1. 2 1 q + −
2. + q
3. – 2q
4. 1 2 q 2 + −

Correct answer: 1 2 q 2 + −

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