If two point charges with charge q are spaced an equal dista

If two point charges with charge q are spaced an equal distance from the origin on the x-axis on opposite sides of the origin, then the electric force on a particle at the origin is zero. Is this equilibrium stable? If yes why; if no why not? No, if the particle is displaced from the origin, then the force tends to push it back to the origin. Yes, if the particle is displaced from the origin, then the force tends to push it back to the origin. No, if the particle is displaced from the origin, then the force tends to push it away from the origin. Yes, if the particle is displaced from the origin, then the force tends to push it away from the origin. The earth has a charge of approximately -7 Times 10^5 C and a pith ball has a charge of approximately 1 Times 10^-9 C. Which of the following describes the relationship between the size of the force the earth exerts on the pith ball and the size of the force the pith ball exerts on the earth? The earth exerts a much larger force on the pith ball. The pith ball exerts a much larger force on the earth. The forces have the same magnitude.

Solution

Answer to first question:

Case 1:if the middle charge is of the same sign as q then the equilibrium is stable and the force tends to push it towards origin. the answer is B.

Case 2 :if the middle charge is of the different sign as q then the equilibrium is unstable and the force tends to push it away from origin. the answer is C.