Choose the correct answer from the following:
If three charged particles are collinear and are in equilibrium, then:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → all the charged particles cannot have the same sign
For the system to be in equilibrium, the net Coulomb force on each of the three charges must be zero. Consider the charge at one end of the line.
If all three charges had the same sign, the two other charges would both repel the end charge, and both repulsions would push it in the same direction, away from them. These two forces cannot cancel, so the end charge could not be in equilibrium.
So for equilibrium the middle charge must have the opposite sign to the two outer charges (the outer ones are attracted inwards by the middle one and pushed outwards by each other).