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Two charges \(+q\) each are kept ' \(2 a\) ' distance apart. A third charge \(-2 q\) is placed midway between them. The …

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Two charges \(+q\) each are kept ' \(2 a\) ' distance apart. A third charge \(-2 q\) is placed midway between them. The potential energy of the system is -

a

\(\frac{ q ^2}{8 \pi \varepsilon_0 a }\)

b

\(-\frac{6 q ^2}{8 \pi \varepsilon_0 a }\)

c

\(\frac{-7 q^2}{8 \pi \varepsilon_0 a }\)

d

\(\frac{9 q^2}{8 \pi \varepsilon_0 a }\)

✓ Correct answer: c)

\(\frac{-7 q^2}{8 \pi \varepsilon_0 a }\)

Explanation

\({U}_{T}=\frac{1}{4\pi {\epsilon }_{0}}\left[-\frac{2{q}^{2}}{a}-\frac{2{q}^{2}}{a}+\frac{{q}^{2}}{2a}\right]\\ =\frac{1}{4\pi {\epsilon }_{0}a}\left[-4+\frac{1}{2}\right]\\ {U}_{T}=\frac{-7{q}^{2}}{8\pi {\epsilon }_{0}a}\\\)

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