Nodes, branches, and loops: circuit vocabulary

The electrical circuit: vocabulary you need to know

Before studying Kirchhoff's laws, you need to know how to name the elements of an electrical circuit.

• A node is a point in the circuit where at least 3 wires meet (a junction of currents).
• A branch is a portion of the circuit connecting two consecutive nodes, containing one or more components (resistor, generator...).
• A loop is a closed path that can be traced starting from a node and returning to it, without passing through the same branch twice.

A concrete example

Imagine a circuit with a generator and two resistors R1 and R2 connected in shunt (in parallel). This circuit has:

Element	Number	Example
Nodes	2	A and B
Branches	3	generator, R1, R2
Loops	2	generator-R1 loop, generator-R2 loop

Current direction and convention

Electric current flows from + to - outside the generator (conventional current direction). Each branch has its own intensity, denoted for example I1, I2, I3. These intensities can be different even though the generator is unique: this is precisely what the node and loop laws allow us to calculate.

Common pitfall

Do not confuse a node with a simple junction of two wires (which is just a point of continuity, with no current sharing). A true node requires at least 3 conductors meeting there.