# 12.1.5 Kirchhoff's Second Law

### 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 conservation of energy
• Below is a circuit explaining Kirchhoff’s second law with the sum of the voltages in the closed series circuit equal to the sum of the e.m.f’s:

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 makes parallel circuits 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

### Author: Ashika

Ashika graduated with a first-class Physics degree from Manchester University and, having worked as a software engineer, focused on Physics education, creating engaging content to help students across all levels. Now an experienced GCSE and A Level Physics and Maths tutor, Ashika helps to grow and improve our Physics resources.
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