Question

A charge $Q$ is placed at the centre of the line joining two point charges $+q$ and $+q$ as shown in figure. The ratio of charges $Q$ and $q$ is

• A. $4$
• B. $1/4$
• C. $-4$
• D. $-1/4$

Answer 1

Answer: (D)

For the system to be in equilibrium,
net force on $q= 0$ or $\frac{Qq}{4\pi\varepsilon_{0}x^{2}}+\frac{qq}{4\pi\varepsilon_{0}\left(2x\right)^{2}}=0$
or $Q=\frac{-q}{4}$ or $\frac{Q}{q}=-\frac{1}{4}$