Question

Point charges $+4q,-q$ and $+4q$ are kept on the $X-axis$ at point $X=0,X=a$ and $X=2a$ respectively

• A. Only $-q$ is in stable equilibrium
• B. None of the charges is in equilibrium
• C. All the charges are in unstable equilibrium
• D. All the charges are in stable equilibrium.

Answer 1

The correct option is D All the charges are in stable equilibrium.

Here focus on $-q$ are

Equal because it is at midpoint between two equal charges, since $+4q$ are also in equilibrium.