JEE Advanced · Physics · 17. Electrostatics
A cubical region of side \(a\) has its centre at the origin. It encloses three fixed point charges, \(-q\) at \((0,-a / 4,0),+3 q\) at \((0,0,0)\) and \(-q\) at \((0,+a / 4,0)\). Choose the correct options(s)

- A The net electric flux crossing the plane \(x=+a / 2\) is equal to the net electric flux crossing the plane \(x=-\) \(a / 2\)
- B The net electric flux crossing the plane \(y=+a / 2\) is more than the net electric flux crossing the plane \(y=-a / 2\).
- C The net electric flux crossing the entire region is \(\frac{q}{\varepsilon_{0}}\)
- D The net electric flux crossing the plane \(z=+a / 2\) is equal to the net electric flux crossing the plane \(x=+a / 2\).
Answer & Solution
Correct Answer
(A) The net electric flux crossing the plane \(x=+a / 2\) is equal to the net electric flux crossing the plane \(x=-\) \(a / 2\)
Step-by-step Solution
Detailed explanation
Due to symmetry, the net electric flux passing through \(x=+\frac{a}{2}\), \(x=-\frac{a}{2}, z=+\frac{a}{2}\) is same
According to Gauss's theorem, net electric flux net electric flux crossing through any closed surface \(\phi=\frac{q_{\text {in }}}{\varepsilon_{0}}=\) \(\frac{-q+3 q-q}{\varepsilon_{0}}=\frac{q}{\varepsilon_{0}}\).
According to Gauss's theorem, net electric flux net electric flux crossing through any closed surface \(\phi=\frac{q_{\text {in }}}{\varepsilon_{0}}=\) \(\frac{-q+3 q-q}{\varepsilon_{0}}=\frac{q}{\varepsilon_{0}}\).
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