The closed loop

For steady conduction in the simple DC circuits studied here, current needs a complete path back to the source. Real circuits can also have transient charging, capacitive coupling or an arc across a gap, so this model should not be read as a universal rule about every electrical phenomenon.

Think of a roundabout with traffic circulating. Cars (electrons) keep moving only because the loop of road is continuous. Block one lane with a barrier and traffic everywhere on that loop grinds to a halt — not just at the barrier.

In a single-path series circuit, opening any connection stops the steady current in that path. A parallel circuit is different: opening one branch can leave the others working.