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PHYSICS · Stage 9 · Chapter 14: Electrical Circuits, Resistance and Power

Physics 14.1 Current in series and parallel circuits — Junction Conservation of Current

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Physics 14.1 Current in series and parallel circuits — Junction Conservation of Current — Alhussan International Academy — Physics (Stages 7–9) notes: Describe series and parallel circuits, how current behaves in each and how to measure current.Series circuit = a circuit with a s…

  • Complete circuit
  • Several lamps in series
  • Same current
  • Not used up
  • Adding components
  • Cell and branches

Part 1 of 5Series circuits

  • Series circuit = a circuit with a single loop.
  • Complete circuit — Current only flows if the circuit is complete, so an open switch is a break in the circuit.
  • Several lamps in series
    • The lamps cannot be turned on and off separately; they are all on or all off.
    • A switch anywhere turns them all on or all off.
    • If one lamp breaks, all the lamps go out.

Part 2 of 5Current in a series circuit

  • AmmeterIt is connected in series to measure current at different points.
  • Same currentThe readings at every point in the loop are the same.
  • Not used upCurrent is not used up; the same number of charges per second pass every point, and the energy they carry is transferred to the components.
  • Adding componentsMore cells in series increase the current, and more lamps in series reduce it.

Part 3 of 5Parallel circuits

  • Parallel circuit = a circuit with more than one loop (branch), also called a branching circuit.
  • Cell and branches — The cell or battery pushes the current around each loop.
  • Independent branches
    • If one lamp breaks, the others still work.
    • The switch in each branch controls the lamps in that branch.
    • Each lamp can be turned on and off independently.
  • Uses — House lights and car headlights are connected in parallel.

Part 4 of 5Current in a parallel circuit

  • JunctionCurrent splits when it reaches a junction of two or more branches.
  • Conservation of currentThe total current flowing into a junction equals the total current flowing out.
  • Battery currentThe current near the battery equals the sum of the currents in all the branches.
  • Adding branchesThe current in each branch stays the same but the total current increases.
  • More currentIncreasing the number of cells increases the current in each branch and the total current.
CircuitCurrent rule
SeriesSame current everywhere
ParallelBranch currents add up to the current from the battery

Part 5 of 5Measuring current

  1. Place one ammeter near the battery and one in each branch of the parallel circuit.
  2. Record all the readings.
  3. Check that the main current equals the sum of the branch currents.
  4. In a series circuit move a single ammeter to different places and show that the reading does not change.
  • Small differences — They are due to the accuracy of the meters.

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