What exactly does it mean when we say that a conductor is grounded? I know it generally means that its potential is zero, but shouldn't the description of potential also give the location of a reference potential? For instance, if a conducting spherical shell is grounded, if its potential is zero, is at the same time the potential at infinity also zero? I get even more confused with flat plates. For eg Consider this prob: "3 large conducting plates are placed parallel to each other. The 2 plates at the sides are grounded. If the charge on the central conductor is Q, how much charge flows from the ground to the 2 extreme end conductors?" Here, where do we take the reference potential? How can we make use of the fact that 2 of the plates are grounded?