Question

Two point charges $-q$ and $-4q$ are located on a line as shown in the figure. Identify the point where a positive charge will not experience any force if placed ?

• A. A
• B. B
• C. C
• D. D
• E. E

Answer 1

Answer: (C)

C

Let the positive charge $(+q)$ is placed at point C.

Distance between $-q$ and point C is $r$ and that between $-4q$ and C is $2r$.

Magnitude of force due to $-q$ $|F_1|=\frac{k{q}^2}{r^2}$

Magnitude of force due to $-4q$ $|F_2|=\frac{kq\left(4q\right)}{(2r{)}^2}=\frac{k{q}^2}{r^2}$

Thus net force at point C $F_{net}=|F_1|-|F_2|=0$

Thus option C is correct.