# Is electric potential of the grounded conductor of a capacitor always zero?

In a spherical capacitor, the net electric potential on the outer grounded conductor due to the positive charge on the inner conductor and the negative charge on the outer conductor is always zero. Is this not correct?

In the same way, is net potential on the grounded negatively charged plate always zero, in case of parallel plate capacitor?

By convention, grounded is synonymous with zero potential. Physically that is not a requirement, however, since only potential difference or potential gradient is of physical significance.

• Yes I understand that. I am pointing that the net potential on the outer conductor of a spherical capacitor is equal to potential at infinity i.e. 0. I am asking if it is true for a parallel plate capacitor. – Physics std Nov 3 at 6:02
• When we say the potential of ground is 0, we don't mean it's the same as the potential at infinity. We mean we're redefining the reference potential for this circuit to be whatever is on this node and calling it zero. – The Photon Nov 3 at 14:41

I'm not sure I understand

In a spherical capacitor, the net electric potential on the outer grounded conductor due to the positive charge on the inner conductor and the negative charge on the outer conductor is always zero.

However, as you say the outer conductor is grounded (and accepting the convention that ground is at zero potential), then, by your own statement the outer conductor is at zero potential, because it is grounded.

Exactly the same is true for grounded plate of a parallel plate capacitor: if it's connected to ground it's at zero; if not, then it's anyone's guess.

• In case of spherical capacitor, the net electric potential on the outer conductor is zero even if it is not grounded. – Physics std Nov 3 at 14:43

Zero potential is whatever you choose it to be. And the meaning of "grounded" can be nebulous (no pun intended). For example, "grounded" could mean the negative terminal of the capacitor is connected to the earth. The earth is typically designated zero potential in an electrical power distribution system. But the term "ground" is sometimes loosely used in electronic circuits to simply mean the location that has been arbitrarily assigned zero potential, that is, the point with respect to which all other potentials are considered positive.

But suppose, for example, you had two charged capacitors connected in series across a battery with no "ground" involved. Which negatively charged plate would you call zero potential? Most would say the plate that is at the same potential as the negative terminal of the battery. Then, of course, the negative plate of the other capacitor would not be at zero potential.

Hope this helps.