Series and parallel circuits — AQA GCSE Physics
Test yourself on Series and parallel circuits with AQA GCSE practice questions.
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Series and parallel circuits explained
Adding a resistor in series puts more opposition into the one path the charge must follow, so the total resistance rises and, for a fixed supply, the current falls.
Read the full explanation
Adding a resistor in parallel does the opposite: it opens an extra route between the same two junctions, so the same potential difference now drives current down both branches. The total current from the supply rises, and since R = V ÷ I a bigger current at an unchanged potential difference means a smaller total resistance, always smaller than the smallest single branch. That is why a hand warmer draws more power when a second heating element is switched in. Series circuits suit testing because one ammeter reading applies to the whole loop and a variable resistor placed in series controls the current everywhere at once.
Your focus
- Explain why a second parallel branch lowers total resistance, naming the extra path and the unchanged supply potential difference.
- Calculate the current, potential difference and resistance at each point of a dc series circuit of two or three resistors.
- Justify placing a variable resistor in series when a test circuit needs its current varied.
Series and parallel circuits exam tips
Marking Points
- one mark for stating that a resistor added in parallel provides another path for the charge
- one mark for the total resistance of the circuit decreasing when that branch is added
- one mark for the current increasing because the potential difference across the battery is unchanged
- one mark for series resistances adding, so that the current falls when a resistor is added in series
Examiner Tips
- 💡For a qualitative explanation, write the chain: extra path, lower total resistance, larger current from the supply.
- 💡'Explain qualitatively' signals that no parallel resistance calculation is ever required here.
- 💡Quote R = V ÷ I when arguing that a larger total current at the same potential difference means a smaller total resistance.
Common Mistakes
- assuming more resistors must always mean more resistance, so predicting a smaller current when a parallel branch is added
- giving a combined parallel resistance larger than one of the individual branch resistances
- explaining the parallel case by saying the potential difference splits between the branches
- allowing the supply potential difference to change during the explanation instead of holding it constant