Electric Charges and Fields - Result Question 6
6. 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
[NEET Kar. 2013, 1995]
(a) $Q / 2$
(b) $-Q / 4$
(c) $Q / 4$
(d) $-Q / 2$
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Answer:
Correct Answer: 6. (b)
Solution:
- (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., $\frac{K Q^{2}}{(2 r)^{2}}+\frac{K Q q}{(r)^{2}}=0$
By solving we get,
$q=-\frac{Q}{4}$.
