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Kirchhoff's Second Law (CIE AS Physics)

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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
  • The energy transferred into the circuit is equal to the energy transferred out of the circuit
  • Below is a circuit explaining Kirchhoff’s second law with the sum of the potential differences across the components in the closed series circuit equal to the sum of the e.m.f’s:

Kirchhoff's second law

Kirchoff's second law in a series circuit, downloadable AS & A Level Physics revision notes

The sum of the potential difference across the individual components are equal to the sum of the e.m.f from the batteries

 

  • In a series circuit, the potential difference is split across all components depending on their resistance
    • The sum of the potential difference across each component is equal to the total e.m.f of the power supply

  • In a parallel circuit, the potential difference is the same across each closed loop
    • The sum of the potential difference in each closed circuit loop is equal to the total e.m.f of the power supply:

Kirchhoff's second law in a series circuit

Kirchoff's second law in a parallel circuit, downloadable AS & A Level Physics revision notes

The total potential difference across the components is the sum of the potential difference across each individual component

  • 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

Loops in a parallel circuit

Loops in parallel circuit, downloadable AS & A Level Physics revision notes

Each circuit loop 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 potential difference
  • If one light breaks, current can still flow through the rest of the lights and appliances

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Ashika

Author: Ashika

Expertise: Physics Project Lead

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.