Kirchhoff's Voltage Law

Kirchhoff's Voltage Law says that if you start at any point in a closed circuit loop and add up all the voltage rises and drops as you go around once, the net change must be zero. This comes from conservation of energy: a charge that returns to where it started cannot have gained or lost net electrical energy over the loop. In practice, sources like batteries provide voltage increases, while components such as resistors, lamps, or motors cause voltage drops.

Use this whenever you need to analyse a circuit loop to find an unknown voltage, current, or component value. It is especially useful for series circuits, multi-loop circuits, and checking whether a proposed circuit calculation is physically consistent.

• Forgetting to choose a sign convention for rises and drops before writing the equation
• Treating voltage as something that gets 'used up' rather than energy being transferred between components
• Leaving out one component in the loop, which makes the sum of voltages incorrect