AQA Physics (8463) 4.2.2 · System
Series and parallel circuits
Change one resistor in a circuit and every reading can move. Can you predict which ones, and which way, before the meters tell you?
Triple Science · Higher tier
Start here · an exam scenario
A 4 Ω resistor and an 8 Ω resistor, one 12 V battery.
Commit first
The two resistors are in series. Which one has the bigger potential difference across it?
In a series circuit there is one loop. The same current passes through every component, and the battery's potential difference is shared between them: bigger resistance, bigger share. Resistances add: Rtotal = R₁ + R₂. In a parallel circuit each branch is connected straight across the battery, so every branch has the full potential difference, and the branch currents add up to the current from the battery. Now change the circuit, one part at a time.
The circuit bench · change one part · change 1 of 4
Swap R₂ for a 20 Ω resistor.
0 of 4 changes
What happens to the ammeter reading?
What happens to the voltmeter reading across R₁?
Sort the rules
Series rule or parallel rule?
Each statement is true of one arrangement only.
Tap a card, then tap the box it belongs in. Tap a placed card to take it back.
Equations
V = I R
potential difference (V, volts) = current (I, amperes) × resistance (R, ohms)
I = V ÷ R · R = V ÷ I
Rtotal = R₁ + R₂
for resistors in series only. In parallel, say the total is less than the smallest; you are not asked to calculate it.
Units first
Current must be in amperes. 1 mA = 0.001 A: divide a milliamp reading by 1000 before inserting it.
Command words in this lesson
- Calculate
- Show every line. If the answer line does not print the unit, give it: it can carry a mark.
- Determine
- Use the circuit diagram or the data to work it out.
- Explain
- Say what changes and why, using current, p.d. and resistance.
Key fact
Series: same current, p.d. shared, Rtotal = R₁ + R₂. Parallel: same p.d., currents add, total resistance less than the smallest branch.
Examiner tip
Key note · AQA 4.2.2 (8463)
Series and parallel circuits
- Series: one path. The same current through every component.
- Series: the supply p.d. is shared. Bigger resistance, bigger share.
- Series: R_total = R₁ + R₂.
- Parallel: every branch has the same p.d. as the supply. Branch currents add up to the total.
- Parallel: total resistance is less than the smallest branch resistance. Adding a branch lowers it.
- V = I R. Convert mA to A first.
Photograph this card. Tomorrow, cover it and say each line first.
Previous and next
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Ask Mr Badmus AI
Not sure whether a circuit is series or parallel?
The bench treats the battery as having no internal resistance and every resistor as fixed, so readings follow the equations exactly. Real meters and cells give slightly lower readings. Circuit symbols follow the AQA symbol sheet.