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5.1.13Chemical Energetics

Parallel Circuits — Cambridge IGCSE Chemistry 0620 Revision Notes & Topical Questions

5 min read 5 parts Lesson 6 of 12 Unit quiz

📚 Cambridge IGCSE Chemistry 0620 Hub / Topical Revision
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Part 1 of 5Rules for Parallel Circuits

5.1.13 Parallel Circuits
Current
  • Current from the supply splits at junctions, and the total current entering a junction equals the total leaving it.
Voltage
  • Every branch of a parallel circuit has the same potential difference as the supply.
Resistance
  • The combined resistance of a parallel circuit is less than the smallest individual resistance, because charge has more than one path.
Equal resistors
  • Two identical resistors connected in parallel give half the resistance of one of them.

Part 2 of 5How Current Splits

1
Charge arriving at a junction is shared between the branches that leave the junction.
2
The current in each branch depends on that branch's resistance, and the branch with the lower resistance takes more current.
3
The branch currents add back together at the next junction to give the total current from the supply.
4
Electrons cannot be created or destroyed, so no current is lost at any junction.

Part 3 of 5Parallel Circuits in Practice

Parallel Circuits in Practice
Mains circuits
  • Household appliances are wired in parallel, so that each one receives the full mains voltage.
Independence
  • If one appliance is switched off, the others keep working, because each has its own branch.
Brightness
  • Identical lamps in parallel each receive the full supply voltage, so each is as bright as a single lamp on the supply.
Total current
  • Adding more branches draws more total current from the supply, because each branch gives charge another path.

Part 4 of 5Worked Example

Question

  • The current entering a junction is 2.0 A.
  • One branch carries 0.75 A.
  • Calculate the current in the other branch.

  1. Step 1: At a junction, the current in equals the current out.
  2. Step 2: The other branch current = total current − known branch current = 2.0 A − 0.75 A.
  3. Step 3: Calculate 2.0 − 0.75 = 1.25 A.

Answer The current in the other branch is 1.25 A.

Part 5 of 5Exam Checklist & Tips

5.1.13 – Key Points for the Exam

  • Parallel circuit A circuit in which the current divides into separate branches that rejoin.
  • Junction A point in a circuit where two or more wires meet.
  • Branch One of the separate paths for current in a parallel circuit.
  • Conservation of charge The principle that the total charge entering a junction equals the total charge leaving it.
  • Combined resistance The single resistance that could replace all the parallel resistors without changing the total current.

Common Mistakes

  • Saying that the current is the same in every branch, even when the branch resistances are different.
  • Stating that adding resistors in parallel increases the total resistance; it decreases the total resistance.
  • Claiming that the potential difference is shared between branches, as it is in series;
    • each branch has the full supply voltage.
  • Forgetting that the branch currents add up to the total current at the junction.

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