Question

Assertion $(A)$ A charge $q$ is placed on a height $h/4$ above the centre of a square of side $b$. The flux associated with the square is independent of side length.
Reason $(R)$ Gauss's law is independent of size of the Gaussian surface.

• A. If both Assertion and Reason are true and Reason is correct explanation of Assertion.
• B. If both Assertion and Reason are true but Reason is not the correct explanation of Assertion.
• C. If Assertion is true but Reason is false.
• D. If both Assertion and Reason are false.

Answer 1

Answer: (A)

In this problem, the concept of electric flux is applied.

We can assume the charge is placed at the centre of the cube. The flux through all the six faces according to the Gauss's law is $\frac{q}{{\epsilon }_0}$.
Thus, flux through one face is $\frac{1}{6}\left(\frac{q}{{\epsilon }_0}\right)$.
Which is independent of size of the cube.