Question

A point charge $+10\mu C$ is at a distance $5cm$ directly above the centre of a square of side $10cm$, as shown in the figure. What is the magnitude of the electric flux through the square?

• A. $1.2\times {10}^{5}N{m}^2/C$
• B. $1.9\times {10}^{5}N{m}^2/C$
• C. $3.2\times {10}^{5}N{m}^2/C$
• D. $4.2\times {10}^{5}N{m}^2/C$

Answer 1

The correct option is B $1.9\times {10}^{5}N{m}^2/C$

Imagine a square cube around the charge with the charge at the centre of the cube and the square being one surface of the cube..
Now apply Gauss law for finding flux through the cube. Divide by 6 to get flux through one face, this is the answer.
$6\varphi =\frac{\varphi }{{ϵ}_0}$ where $\varphi =$ flux through one of the faces of square cube.
$\varphi =1.9\times {10}^{5}N{m}^2/C$