Question

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

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

Answer 1

Answer: (B)

$-3\,\overrightarrow{E}$

Answer 2

Given, point charges: $Q$ and $-3 Q$ electric field at $Q=\vec{E}$ Let the electric field around $Q$ ? And electric fidd around $-3 Q=E_{2}$. $E_{1}=\frac{R Q}{r^{2}}=\bar{E} \quad\left[r=\operatorname{small}_{\text {around }} Q_{\text {distance }}\right] \text {. }$ similarly, $\begin{aligned} E_{2} &=\frac{k(-3 Q)}{r^{2}} \\\ &=\frac{-3 k Q}{r^{2}}=(-3)\left[\frac{k Q}{r^{2}}\right] . \\\ E_{2} &=-3 \vec{E} \end{aligned}$ Thus, the electric field at location of $-3 Q$ charge will be $-3 \vec{E}$.