Four equal charges `Q` are placed at the four corners of a square of each side is 'a'. Work done in removing a charge `-Q` from its centre to infinity is

Three equal charges Q are placed at the three corners of an equilateral triangle of side length a. Work done in shifting a charge q from infinity to the centroid of the triangle is

Four equal charges q are placed at the four corners of a square of length of each side a. What charge should be kept at the middle of the square so that the system is in equilibrium ?

Four identical point charges q are placed at four corners of a square of side a. Find the potential energy of the charge system. .

Four identical point charges q are placed at four corners of a square of side a. Find the potential energy of the charge system. .

Equal charges Q are placed at the four corners A, B, C, D of a square of length a. The magnitude of the force on the charge at B will be

Equal charges Q are placed at the four corners A, B, C, D of a square of length a. The magnitude of the force on the charge at B will be

Equal charges q are placed at the four corners A,B,C,D of a square of length a . The magnitude of the force on the charge at B will be