A charge q is placed at the center of the line joining two equal charges Q. The system of three charges will be in equilibrium if q is equal to
Two free charges q and 4q are placed at a distance d apart. A third charge Q is placed between them at a distance x from charges q such that the system is in equilibrium.Then
Two positive charges of equal magnitude q are placed as shown in the figure. A negative charge of magnitude Q is placed at the centre of line joining them. The value of Q for the whole system to be in equilibrium.