Physics
Physics
Problem
A charge of +6 µC is fixed at x = 0 m and a charge of –3 µC is fixed at x = 0.30 m on a straight line in vacuum. At what distance from the +6 µC charge, measured along the line and on the side of the –3 µC charge, will a small positive test charge experience zero net electrostatic force? a) b) c) d)Intuitive explanation
You're looking for an equilibrium point where the electric forces from both charges cancel out. Since the test charge is positive, the +6 µC charge repels it while the –3 µC charge attracts it—so balance is possible on the far side of the negative charge. The key insight is that at equilibrium, the magnitudes of both forces must be equal, which means you can set up a ratio using Coulomb's law and solve for the unknown distance. Pay attention to which direction each force points and remember that the weaker charge (–3 µC) must be closer to the test point for the forces to have equal strength.
Intuitive explanation
You're looking for an equilibrium point where the electric forces from both charges cancel out. Since the test charge is positive, the +6 µC charge repels it while the –3 µC charge attracts it—so balance is possible on the far side of the negative charge. The key insight is that at equilibrium, the magnitudes of both forces must be equal, which means you can set up a ratio using Coulomb's law and solve for the unknown distance. Pay attention to which direction each force points and remember that the weaker charge (–3 µC) must be closer to the test point for the forces to have equal strength.