Question

Three point charges of + 2 µC, – 3 µC and – 3 µC are kept at the vertices A, B and C respectively of an equilateral triangle of side 20 cm as shown in figure. What should be the sign and magnitude of charge to be placed at the midpoint M of side BC so that charge at A remains in equilibrium?

Answer 1

Let charge placed at M be q_M. The forces acting on charge (q_A = + 2µC) are F_AB, F_AC and F_AM as shown in figure.

For equilibrium of charge q_A: the resultant of \(\vec F\)_AB and \(\vec F\)_AC  must be equal and opposite to \(\vec F\)_AM.