Kirchhoff's Second Law (OCR AS Physics): Revision Note

Kirchhoff's Second Law

• Kirchhoff’s second law states that:

  The sum of the e.m.f’s in a closed circuit equals the sum of the potential differences

• This is a consequence of the conservation of energy

The sum of the voltages are equal to the sum of the e.m.f from the batteries

• In a series circuit, the voltage is split across all components depending on their resistance

  • The sum of the voltages is equal to the total e.m.f of the power supply

• In a parallel circuit, the voltage is the same across each closed loop

  • The sum of the voltages in each closed circuit loop is equal to the total e.m.f of the power supply:

• A closed circuit loop acts as its own independent series circuit and each one separates at a junction

  • A parallel circuit is made up of two or more of these loops

Each circuit loops acts as a separate, independent series circuit

• This is why parallel circuits are incredibly useful for home wiring systems

  • A single power source supplies all lights and appliances with the same voltage

  • If one light breaks, voltage and current can still flow through for the rest of the lights and appliances