A charge ‘q’ is placed at the centre of the line joining

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A charge ‘q’ is placed at the centre of the line joining two equal charges ‘Q’. The system of the three charges will be in equilibrium if ‘q’ is equal to

1. Q/2
2. – Q/4
3. Q/4
4. – Q/2

Correct Option: B

The system of three charges will be in equilibrium.

For this, force between charge at A and B + force between charge at point O and either at A or B is zero.

i.e. ,	KQ²	+	KQq	= 0
	r²		(r / 2)²

By solving we get,

q = -	Q
	4