I–V Characteristics Virtual Lab: Resistor, Lamp and Diode

Updated 2026-10-07

This I–V characteristics virtual lab matches the AQA GCSE Physics required practical on the current–potential difference graphs of a resistor, a filament lamp and a diode. Students set a variable d.c. supply, read a voltmeter across the component and an ammeter in series with it, and record readings in both directions. One lesson gives three shapes from students' own readings: a straight line, a curve that flattens, and a one-way switch-on near 0.6 V.

I–V characteristics – resistor, filament lamp, diode and LED

Curriculum links

AQA GCSE Physics (8463) 4.2.1.4 (resistors) and required practical 4: measuring how the current varies with potential difference for a filament lamp, a diode and a resistor kept at constant temperature. In Combined Science: Trilogy the same content is 6.2.1.4.

Simulic is not affiliated with or endorsed by AQA.

Before the lab (5 min)

Ask students to commit to a prediction, on paper or as question 1 of the class link:

"You raise the potential difference across a filament lamp from 0 to 6 V and plot I against V. What shape will the graph be?"

Expect many students to draw a straight line, because "that's Ohm's law".

Method in the simulation

For each reading: close switch S, wait for steady meters, press Record reading, then press Open switch S before changing the supply. Supply E is the power supply setting; the voltmeter shows the potential difference V across the component, which is a little less.

Resistor. Choose Fixed resistor and set Resistance R to 47 Ω. Record readings at Supply E = 1.0, 2.0, 3.0, 4.0, 5.0 and 6.0 V (slider or − / + buttons).
Press Reverse supply and repeat to get negative readings.
Filament lamp. Choose Filament lamp (6 V, 0.3 A) and repeat steps 1 and 2. Do not go above its rated 6 V.
Diode. Choose Silicon diode with a 330 Ω Protective resistor. Record readings at E = 0.5, 1.0, 2.0, 3.0, 4.0 and 6.0 V, and tick Zoom in around the origin. Then reverse the supply at 3.0 V.
Tap any point to see R = V/I. Tick Show reference curve to compare your points with the model.

Supply E (V)	1.0	2.0	3.0	4.0	5.0	6.0
V across lamp (V)
I (mA)
R = V/I (Ω)

the filament lamp graph with points in both quadrants and the dashed line from the origin to the point at 5.82 V

Expected results

All readings come from the simulation. Each meter has a small random error, so the last digit can differ by 1.

Filament lamp:

Supply E (V)	1.0	2.0	3.0	4.0	5.0	6.0
V (V)	0.92	1.89	2.87	3.86	4.84	5.82
I (mA)	138.0	177.2	211	242	270	296
R (Ω)	6.6	10.7	13.6	15.9	17.9	19.7

The curve gets flatter and R triples between 1 V and 6 V. Reversed readings mirror these through the origin.

Resistor (47 Ω): at E = 6.0 V the meters read 5.92 V and 125.7 mA, so R = 47.1 Ω. All points lie on a straight line through the origin. If switch S stays closed for a minute at 6 V, the resistor warms to about 56 °C and R drifts to about 48.7 Ω.
Silicon diode (330 Ω): 0.44 V and 0.19 mA at E = 0.5 V; 0.53 V and 1.41 mA at 1.0 V; 0.61 V and 7.2 mA at 3.0 V; 0.65 V and 16.2 mA at 6.0 V. The current rises steeply while V hardly changes. Reversed at 3.0 V: −3.00 V and 0.00 mA.
Red LED (330 Ω): 1.80 V and 3.6 mA at E = 3.0 V. It starts to conduct near 1.7 V instead of about 0.5 V.

Questions for students

(Prediction, asked again after the lab) What shape is the I–V graph of a filament lamp from 0 to 6 V?
For the fixed resistor to give a straight line through the origin, which variable must be kept constant?
With the silicon diode, a 330 Ω protective resistor and E = 3.0 V, what does the voltmeter read?
For the lamp, calculate R = V/I at E = 1.0 V and at E = 6.0 V. How many times larger is R at 6.0 V?
Explain why the resistance of a filament lamp rises as the potential difference across it increases.

Answers for teachers: (1) A curve through the origin that gets less steep. (2) The temperature of the resistor. (3) 0.61 V (accept 0.59–0.63). (4) About 6.6 Ω and 19.7 Ω, so about 3.0 times (accept 2.8–3.1). (5) A larger current heats the filament more. The metal ions vibrate more, the electrons collide with them more often, and the resistance goes up.

Common misconceptions

"Every component obeys Ohm's law." Only the resistor at constant temperature does. The lamp's R goes from 6.6 Ω to 19.7 Ω in one experiment.
"Reversing the supply just makes the current negative." True for the resistor and the lamp. The diode reads 0.00 mA at −3.00 V: its R = V/I is about 84 Ω forwards at E = 3.0 V and almost infinite in reverse.

Extension

Why a protective resistor? Set the protective resistor to None and raise E in 0.1 V steps. The current is 5.5 mA at E = 0.6 V and 311 mA at 1.0 V, and the diode burns out once it passes 1 A (near E = 1.6 V). With 330 Ω at 6 V, students can calculate the safe current: (6 − 0.65) ÷ 330 ≈ 16 mA.
Hot resistor. Set R = 10 Ω and E = 12 V and leave the switch closed. The temperature label climbs and the current falls until the resistor burns out. Link it to P = VI.

FAQ

Why does the voltmeter read less than the supply setting?

The supply and ammeter have 0.6 Ω of internal resistance, and with the diode most of E is across the protective resistor. Plot the voltmeter reading, not E.

Why are the diode readings so close together?

Once a silicon diode conducts, a small change in V gives a large change in I. Add readings between E = 0.5 and 2.0 V and zoom in to see the bend.

Does this replace the wet practical?

Not for AQA: required practicals must still be done by hand. Use the simulation to plan, rehearse or analyze the results. See virtual labs vs physical labs.