Question

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 1

Answer: (A), (C), (D)

Net flux through the cubical region $=\frac{-q+3 q-q}{\varepsilon_{0}}=\frac{q}{\varepsilon_{0}}$
The flux passing through the faces $x =\frac{- a }{2}, x =+\frac{ a }{2}$ and $z =+\frac{ a }{2}$ are same due to symmetry.