StellarA simple circuit contains a source of electric potential difference, conducting wires, and one or more circuit elements such as a resistor or bulb. In an ideal circuit, the battery provides a fixed potential difference and the wires have negligible resistance. Charge does not get “used up” in the circuit. Instead, the electric field established by the battery drives charge around the loop, and circuit elements transform electrical energy into other forms such as thermal energy or light.
The most important qualitative ideas in simple circuits are continuity of current in a single loop and the role of potential difference. In a single-loop steady-state circuit, the current is the same everywhere. What changes across a resistor is the electric potential. A battery raises electric potential, and a resistor lowers it. This provides the first clear energy picture of circuits: the battery increases the electric potential energy per unit charge, and the resistor converts that energy into other forms.