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MHT CET 2021 (23 Sep, Shift 2) · Electrostatic Potential Energy

Electrostatic Potential Energy question from MHT CET 2021 (23 Sep, Shift 2)

Q45MHT CET 2021 · 23 SEP · SHIFT 2Medium

Electrostatic Potential Energy

Three charges $-q, Q$ and $-q$ are placed at equal distances on a straight line. If the total potential energy of the system of three charges is zero then the ratio $\frac{Q}{q}$ is

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Answer: (c)

Let the spacing be $d$ : $Q$ is in the middle, the two $-q$ charges are $2d$ apart.
$U = k\left[-\frac{qQ}{d} - \frac{qQ}{d} + \frac{q^2}{2d}\right] = 0$
$2Q = \frac{q}{2} \Rightarrow \frac{Q}{q} = \frac{1}{4}$
So the answer is (c) $1:4$ .

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