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Physics 11–12 · Year 11

Current-voltage characteristics of a resistor, a filament lamp and a diode

Module 4: Electricity and Magnetism (Electric Circuits)

Practical, model not builtLow risk

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The idea

A metallic resistor at constant temperature obeys Ohm's law, while a heating filament and a diode do not, which shows the law's usefulness and its limits.

What you need

  • Variable DC supply 0 to 12 V, or a 12 V supply with a rheostat as a potential divider
  • Digital ammeter (0 to 1 A) and voltmeter, 10 ohm 5 W resistor, 12 V 6 W filament lamp, silicon diode with a 100 ohm protective resistor
  • Connecting leads, switch

How to do it

  1. Connect the resistor with the ammeter in series and the voltmeter across it; record I for V from 0 to 6 V in 0.5 V steps, then reverse the supply.
  2. Repeat for the lamp up to 12 V, waiting for the reading to settle at each step.
  3. Repeat for the diode with its series resistor, forward then reverse, in 0.1 V steps around the knee.
  4. Plot I against V for each component on the same axes and compute R = V/I at several points.

What you should see

The resistor gives a straight line through the origin: 10.0 ohms at every point (0.600 A at 6.0 V). The lamp's curve bends over: its resistance climbs from a much lower cold value to 24 ohms at 12 V, 0.50 A (6.0 W) as the filament heats. The diode passes negligible current until about 0.6 to 0.7 V forward, then the current rises steeply, and it passes almost nothing in reverse.

What changes

What you change
potential difference across the component
What you measure
current through it
What you keep the same
  • temperature for the resistor (short readings)
  • same meters
  • same component

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

  • Every component obeys Ohm's law; only some do, and only at constant temperature.
  • A steeper I-V line means a larger resistance; on I against V axes a steeper line means a smaller resistance.

Safety card

Low riskLearners carry it out

Hazards

  • hot lamp and resistor
  • diode destroyed without its series resistor

Controls

  • switch off between readings
  • keep the 100 ohm resistor in the diode circuit

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 2027PH11-11PH11/12-5
  • 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-04
  • Australian Curriculum v9No Australian Curriculum v9 code is listed.

Sources

The pages the author read to write this activity.

  1. www.nsw.gov.au/sites/default/files/noindex/2025-03/physics-stage-6-syllabus-2017.docx
  2. 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
  3. phet.colorado.edu/en/simulations/circuit-construction-kit-dc
  4. www.bipm.org/en/measurement-units/si-defining-constants
  5. curriculum.nsw.edu.au/learning-areas/science/physics-11-12-2025/outcomes

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