直流电池

When an electric field is applied to an isolated conductor, current initially flows. However, positive and negative charges accumulate at opposite ends, creating an equal and opposite electric field that cancels the applied field. This stops current flow because the total electric field becomes zero. A closed circuit with a battery is required to maintain continuous current.

A battery acts like a pump, using chemical energy to provide a non-electrostatic force that pushes electrons from the positive to the negative terminal against the electrostatic force. This force maintains the potential difference between terminals, converting chemical energy into electrical energy and enabling continuous current flow through a closed circuit.

Two beakers with different water levels connected by a pipe demonstrate potential difference. Water flows from high to low level until levels equalize. Similarly, in circuits, potential difference drives charge flow. A water pump maintains the difference for continuous flow, just as a battery maintains electrical potential difference for steady current.

Charges lose potential energy passing through conductors. For charges to continue flowing from higher to lower potential, an external agent must return them from lower to higher potential, completing the loop. An open circuit cannot maintain consistent charge flow because charges cannot return to their starting point and potential energy cannot be restored.

A battery converts chemical energy into electrical potential energy through internal non-electrostatic forces. These forces push electrons uphill against the electrostatic field, doing work per unit charge. This work, called electromotive force, transfers energy into the circuit, enabling current to flow from lower to higher potential within the battery.

Electromotive force sources include batteries, electric generators, solar cells, thermocouples, and fuel cells. All these devices convert energy from various sources—mechanical, chemical, thermal, or other forms—into electric potential energy that transfers into circuits to drive continuous current flow through the system.

After reaching the negative terminal, electrons move toward the positive terminal through the external circuit to complete the closed loop. This continuous movement, driven by the battery's maintained potential difference, constitutes the steady current flowing through the circuit and returning to the battery's positive terminal.