Question

Two point charges Q and $-3$Q are placed at a certain distance apart. Let the electric field at the location of Q be $\overrightarrow{E}$, then that at the location of $-3$Q will be :

• A. $3\overrightarrow{E}$
• B. $-3\overrightarrow{E}$
• C. $\frac{\overrightarrow{E}}{3}$
• D. $-\frac{\overrightarrow{E}}{3}$

Answer 1

The correct option is D $-\frac{\overrightarrow{E}}{3}$

The electric field is from $Q$ to $-3Q$, i.e. from positive to negative charge. Electric field at location of $Q$ is $\overrightarrow{E}=k(-3Q)\overrightarrow{n}/d^2$ where $D$ is the distance between the two charges. $\overrightarrow{n}$ is the direction vector. Electric field at location of $-3Q$ is $k\left(Q\right)\overrightarrow{n}/d^2=\overrightarrow{-E/3}$