# What is voltage in a circuit?

1. What is voltage in a circuit?

I know potential difference is the difference of potential energy of two points in a space affected by an electric field per unit charge.

1. Why is there voltage in a circuit with a battery?

2. To have a voltage there must have an electric field, where is the field in a battery circuit and how is it created?

• Voltage is a name for potential difference – Steeven Oct 31 '16 at 6:59

The term Potential is not restricted to electrical fields. Potential is synonymous with the ability to do work. If potential exists in a physical system then the system is not necessarily in equilibrium: energy at a higher potential state will flow to the lower state.

A ball setting on a shelf has potential in a gravitational field. A small nudge converts the potential to the kinetic energy of motion until it hits the ground.

A battery creates potential by an electrochemical process. Completing a conductive path between electrodes starts the reaction, and electrons flow from the higher to lower potential.

• "where is the field in a battery circuit and how is it created?" As docscience states once you release the potential you have the field. – william deets Oct 31 '16 at 3:20
• A battery's own field is insufficient for the movement of charges around the entire circuit. There are electrostatic fields at the bends of wires, which provide the intermediary field for transport. – Lelouch Oct 31 '16 at 3:49
• Lelouch -> what creates these electrostatic fields at the bends of wire? Also, what are bends of wire? the curve? – gigi Dec 20 '16 at 0:30

Inside a battery there is a chemical reaction which in effect moves electrons from one terminal (called positive) of the battery to the other (called negative).
In turn those charges on the terminals set up an electric field in opposition to the movement of electrons which eventually stops any further electrons moving.
There is now a potential difference across the terminals of the battery. This is also called the voltage across the battery terminals.

Connecting a conducting path across the terminals of the battery sets up an electric field inside the conductor and mobile charge carriers then move under the influence of this electric field.
The voltage across the terminals of the battery being maintained by the chemical reaction within it.

• I'm not sure if I understand correctly so could you say OK if I do? What I understand is that the accumulation of electrons in the negative terminal and lack of them in the positive terminal creates an electric field everywhere outside the battery (in the air or in a wire) but only a wire can create electricity with this field because it is easier to move electrons in a wire than in air. – gigi Dec 19 '16 at 21:17
• Only a current flows through the wires because there are mobile charge carriers available whose movement constitutes an electric current. Air is effectively an insulator as is no mobile charge carriers. – Farcher Dec 19 '16 at 21:54
• But with this logic, a wire could conduct electricity even if it is at a certain distance from the battery, since the negative electric field from the negative terminal can pass through air (for example, two electrons can repulse each other even if they are at a certain distance) ? Is there something I don't understand correctly? – gigi Dec 19 '16 at 22:10
• You are correct in that electrons will move along the conductor and accumulate at one end of the air gap with a deficit of electrons on the other side of the air gap. This will continue until the electric field inside the conductor is zero but there is an electric field across the air. No current can flow across the air gap even though there is an electric field because there are no mobile charge carriers in the air. The charges which are at the ends of the conductor set up an electric field in opposition to that produced by the chemical reaction inside the battery cont'd – Farcher Dec 20 '16 at 3:35
• Cont'd The ends of the conductor can be though of as the new terminals of the battery. – Farcher Dec 20 '16 at 3:36