Physics 11–12 · Year 11
Series and parallel circuits: current and voltage rules from measurements
Module 4: Electricity and Magnetism (Electric Circuits)
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The idea
Charge is conserved at every junction and energy is conserved around every loop, which gives the current and voltage rules for series and parallel resistors.
What you need
- 6 V DC supply, 100 ohm and 200 ohm resistors (0.5 W), two digital multimeters, leads, breadboard or terminal board
- Two 6 V lamps for the qualitative comparison
How to do it
- Predict the currents and voltages for 100 and 200 ohms in series at 6.0 V, then build it and measure the current at three points and the voltage across each resistor (the NSW Department of Education Module 4 guide predict-then-test activity).
- Rebuild in parallel; measure the current in each branch and in the supply lead, and the voltage across each resistor.
- Compare sums of currents at the junction and sums of voltages around the loop with the supply values.
- Compute the effective resistance in each case from the supply current.
What you should see
Series: 0.020 A everywhere, 2.0 V across 100 ohms and 4.0 V across 200 ohms (sum 6.0 V), total 300 ohms. Parallel: 6.0 V across both, 0.060 A and 0.030 A in the branches, 0.090 A from the supply, effective resistance 66.7 ohms. The measured currents at the junction and the voltages around each loop add up to the supply values within the meters' stated accuracy; differences from the predicted values come from the resistors' tolerance and the supply's internal resistance.
What changes
- What you change
- circuit arrangement
- What you measure
- branch currents and component voltages
- What you keep the same
- supply voltage
- same resistors
- same meters
Common misconceptions
Each of these ideas is wrong, and the activity is a chance to test it.
- Current is used up as it passes through resistors; the current flowing out of a series resistor equals the current flowing in.
- The battery supplies a fixed current whatever the circuit; it supplies a fixed voltage and the circuit sets the current.
Safety card
Hazards
- warm resistors
Controls
- 0.5 W resistors at 6 V stay below rating
Note
Record the activity in RiskAssess (https://www.riskassess.com.au/) and follow the Science ASSIST risk management information sheet (https://asta.edu.au/resource/ais-risk-management-and-risk-assessment/).
Curriculum references
The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.
- Physics Stage 6 Syllabus (2017), current: Year 11 until the end of 2026, Year 12 until Term 3 2027PH11-11PH11/12-1PH11/12-5
- Physics 11-12 Syllabus (2025), not yet taught: Year 11 from Term 1 2027, Year 12 from Term 4 2027, first HSC examination 2028PY-11-03PY-11WS-05
- Australian Curriculum v9No Australian Curriculum v9 code is listed.
Sources
The pages the author read to write this activity.
- www.nsw.gov.au/sites/default/files/noindex/2025-03/physics-stage-6-syllabus-2017.docx
- education.nsw.gov.au/content/dam/main-education/teaching-and-learning/curriculum/key-learning-areas/science/media/documents/physics-s6-module-4-guide-electricity-and-magnetism.docx
- phet.colorado.edu/en/simulations/circuit-construction-kit-dc
- curriculum.nsw.edu.au/learning-areas/science/physics-11-12-2025/outcomes