Edexcel A Level Physics:复习笔记3.5 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