Question

Two point charges $q$ and $-2q$ are placed some distance $d$ apart. If the electric field at the location of $q$ due to $-2q$ is $E$, than at the location of $-2q$ due to $q$ is ( No external Field is present )

• A. $-\frac{E}{2}$
• B. $-2E$
• C. $\frac{E}{2}$
• D. $-4E$

Answer 1

Answer: (A)

$-\frac{E}{2}$

Let the distance between two charges be $d$.
Considering the electric field of $-2q$.
$|E|=|\frac{k(-2q)}{r^2}|=\frac{2kq}{r^2}$

The direction of this electric field will be towards the charge $-2q$
Considering the electric field due to $q$ only:
Electric field $=|\frac{kq}{r^2}|=\frac{E}{2}$

The direction of this electric field will be away from the charge $q$ which is same as direction of electric field due to charge $-2q$

Hence $\frac{E}{2}$ will be the right answer.