Question

Two charges of $-2Q$ and $Q$ are located at points $(a,0)$ and $(4a,0)$ respectively. What is the electric flux through a sphere of radius $3a$ centred at the origin?

• A. $\frac{Q}{{ϵ}_0}$
• B. $\frac{-Q}{{ϵ}_0}$
• C. $\frac{-2Q}{{ϵ}_0}$
• D. $\frac{3Q}{{ϵ}_0}$

Answer 1

The correct option is C $\frac{-2Q}{{ϵ}_0}$

We know that flux$=\varphi =\frac{q}{{ϵ}_o}$ where $q$ is charge inside the closed surface area and flux due to charge outside is zero.

Here, charge inside$=q=-2Q$

Hence, flux$=\varphi =\frac{-2Q}{{ϵ}_o}$

Answer-(C)