Which one of the following graphs represents the variation of electric potential with distance r from the centre of a non-conducting charged sphere of radius R?
Four charges equal to + Q are placed at the four corners of a square and a charge ($$-$$q) is at its centre. If the system is in equilibrium, then the value of $$-$$q is
An electric dipole is placed at an angle of 30$$^\circ$$ in a non-uniform electric field. The dipole will experience