Question

The point charge $Q$ and $-2Q$ are placed of some distance apart. If the electric field at the location of $Q$ is $E$. Then the electric field at the location of $-2Q$ will be

• A. - 2E
• B. -E
• C. $-\frac{5E}{2}$
• D. $-\frac{E}{2}$

Answer 1

Answer: (D)

Electric field at location of Q is due to -2Q.
$E_Q=\frac{-K.2Q}{r^2}=E$
Electric field at location of - 2Q is due to Q.
$\therefore E_{-2Q}=\frac{KQ}{r^2}$
$\Rightarrow \frac{E_{-2Q}}{E_Q}=\frac{\frac{KQ}{r^2}}{-K\frac{2Q}{r^2}}$
$\Rightarrow E_{-2Q}=-\frac{E_Q}{2}=\frac{-E}{2}$