An electric circuit is a connected arrangement of components through which charge can move and electrical energy can be transferred.

A circuit diagram represents the electrical connections rather than the physical layout.

Nodes and branches

A node is a set of points connected by ideal conductors and therefore treated as having the same electric potential. A branch is a path between nodes containing one or more circuit elements.

Voltage and current

Current describes charge flow through a branch. Voltage describes the potential difference between two nodes.

These are different kinds of quantities: current is associated with a path through a component, while voltage compares two points.

Sources and loads

An ideal voltage source maintains a specified potential difference. Components such as resistors can receive electrical energy from the circuit and convert it into other forms.

Open and closed paths

A broken connection can prevent a steady current path even when voltage exists across the open points. A closed conducting network provides paths through which current can flow.

Circuit analysis replaces the detailed electromagnetic fields inside wires and components with a lumped model of currents, voltages and component relationships.