Energy Conservation in Circuits (Edexcel International A Level Physics)

Energy Conservation in Circuits

The Electrical Voltages Rule (Kirchhoff's Second Law)

• Energy is never used up or lost in a circuit, since everything follows the Law of Conservation of Energy

• The electrical voltages rule is defined as:

  The sum of the e.m.f.s in a closed circuit loop is equal to the sum of the potential differences around that loop

• Each closed circuit loop can be treated like a series circuit

• A typical circuit might have a setup where  E₁ + E₂ = V₁ + V₂ where:

  • E₁ and E₂ represent the e.m.f.s in the closed loop

  • V₁  and V₂ represent the potential differences in the closed loop

The sum of the voltages is equal to the total 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:

The sum of the p.ds in each closed loop is equal to the total e.m.f of the power supply

• A closed-circuit loop acts as its own independent series circuit

• Each loop 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