An electron is fixed at the position x = 0, a second charge q is place to the right of the electron fixed a distance x = 4 x 10-9 m. A proton is then placed between the electron and the charge a distance xp = 1 × 10-9 m. Find what magnitude and sign must be for the charge q, to ensure that the proton is in equilibrium.

An electron is fixed at the position x = 0, a second charge q is place to the right of the electron fixed a distance x = 4 x 10-9 m. A proton is then placed between the electron and the charge a distance xp = 1 × 10-9 m. Find what magnitude and sign must be for the charge q, to ensure that the proton is in equilibrium.