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 $- 2 Q$ will be

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