Question

A point charge Q is placed just outside a cube of side 'a' near corner H. Flux of electric field associated with face ABCD is

• A. $0$
• B. $\frac{Q}{4{\epsilon }_0}$
• C. $\frac{Q}{24{\epsilon }_0}$
• D. $\frac{Q}{8{\epsilon }_0}$

Answer 1

The correct option is C $\frac{Q}{24{\epsilon }_0}$

If charge is placed at corner(not just outside), $\frac{Q}{8}$ charge is inside cube.
Now, if it is placed just outside the corner, the net flux through the cube will now be zero, but the flux through surface ABCD will approximately be equal to the same.
So, ${\varphi }_{ABCD}=\frac{Q}{8\times 3{\epsilon }_0}$
$=\frac{Q}{24{ϵ}_0}$.