Question:

A point charge $+q$ is placed at the centre of a cube of side $L$. The electric flux emerging from the cube is

Updated On: Jan 19, 2024
  • $\frac{q}{\varepsilon_{0}}$
  • Zero
  • $\frac{6qL^{2}}{\varepsilon_{0}}$
  • $\frac{q}{6L^{2}\varepsilon_{0}}$
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The Correct Option is A

Solution and Explanation

Since the charge is placed at the centre of the cube, so the electric flux lines move out equally from all sides of the cube. Thus the electric flux emerging from the cube is equal to $\frac{q}{\varepsilon_{0}}$.
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Concepts Used:

Gauss Law

Gauss law states that the total amount of electric flux passing through any closed surface is directly proportional to the enclosed electric charge.

Gauss Law:

According to the Gauss law, the total flux linked with a closed surface is 1/ε0 times the charge enclosed by the closed surface.

For example, a point charge q is placed inside a cube of edge ‘a’. Now as per Gauss law, the flux through each face of the cube is q/6ε0.

Gauss Law Formula:

As per the Gauss theorem, the total charge enclosed in a closed surface is proportional to the total flux enclosed by the surface. Therefore, if ϕ is total flux and ϵ0 is electric constant, the total electric charge Q enclosed by the surface is;

Q = ϕ ϵ0

The Gauss law formula is expressed by;

ϕ = Q/ϵ0

Where,

Q = total charge within the given surface,

ε0 = the electric constant.