Required Practical – Simulation of Resistance and Change in length of wire

What the simulation does

This is an interactive 3D lab bench for the GCSE Physics required practical “investigate how the resistance of a wire changes with its length.” It runs as a two-act experience in the ClassAdapt house style.

Act 1 — build and measure. Pupils work through a seven-step circuit build on a realistic bench: a 6 V supply, switch, ammeter and a length of nichrome wire taped along a metre ruler, wired as a series loop, with a voltmeter connected in parallel across the test length. They drag a crocodile clip along the ruler to set the length (it snaps to 20, 40, 60, 80 and 100 cm), close the switch, read V and I off the 3D meters, and work out R = V ÷ I. Charge dots flow faster along shorter wire, giving a non-colour cue for higher current. The fair-test controls (same wire, same thickness, same supply; read quickly so the wire doesn’t heat up) are built into the on-screen prompts.

Act 2 — plot and conclude. Once all five lengths are recorded, the results table fills in and a live graph of resistance against length is revealed point by point, landing on the conclusion: a straight line through the origin, R ∝ L — double the length, double the resistance.

The physics is exact: because the voltmeter reads across the wire only, R = V ÷ I recovers ρL/A precisely, giving readings of 3.9 / 7.7 / 11.6 / 15.4 / 19.3 Ω. The whole thing carries the full Adapt accessibility suite (dark theme, Irlen overlays, CVD filters, reading ruler, dyslexia spacing, text scaling, projector mode, reduce/slow motion, and a buttons-only mode for pupils who can’t drag), and works from phone up to projector.

Suggested class activity — a 50-minute lesson

Do, then think works well here because the sim removes the fiddly circuit-building and lets pupils focus on the measuring, the pattern and the reasoning.

Starter (5 min). Project the sim on the board. Show the circuit at 20 cm and again at 100 cm without commentary. Ask: “Same wire, same battery — what changed, and what do you predict happens to the current?” Take a show of hands on whether current goes up or down, and get one pupil to justify each side. This surfaces the intuition before any numbers appear.

Prediction (5 min). Before running it, pupils sketch on mini-whiteboards what they think a graph of resistance against length will look like — a curve, a straight line through the origin, a straight line with an intercept, or a flat line. Keep these; you’ll return to them.

Main investigation (20 min). In pairs on devices, or as a teacher-led whole-class run if you have one screen, pupils work through all five lengths and copy the results table into their books. The key discipline to insist on: record V and I for every length and calculate R themselves rather than just reading the value off — the sim shows R = V ÷ I so they can self-check, but the calculation is the learning. Pupils who struggle with the dragging can switch on “buttons only” mode in the accessibility menu.

Consolidation (10 min). Pupils plot resistance against length on graph paper (or you reveal the sim’s Act 2 graph and they compare). Draw the line of best fit, confirm it passes through the origin, and write the conclusion in the form “R is directly proportional to L.” Then revisit the whiteboard predictions — who was right, and why did the straight-line-through-origin shape win?

Plenary and stretch (10 min). Three questions of rising demand:

• Recall: State the relationship between resistance and length.
• Apply: If 60 cm gives 11.6 Ω, predict the resistance of 120 cm, and explain your reasoning using proportionality.
• Explain / stretch: Why does a longer wire have more resistance? (Guide them to: more length means the charge undergoes more collisions with the metal ions, so more opposition to flow.) For your strongest pupils, ask why the line goes through the origin — what would zero length physically mean?

Assessment and homework. The plotted graph plus a written conclusion and one fair-test justification (“name two things you kept the same and why”) makes a clean exit-ticket. For homework, ask pupils to design — on paper — how they’d adapt the same method to investigate a different variable, such as the wire’s thickness, naming what they’d change, measure and control.

A couple of teaching notes worth flagging: the current at 20 cm runs to about 1.4 A, which is a genuine talking point — real thin nichrome would warm up fast, which is exactly why the method says read quickly and switch off, and why heating would spoil the fair test if you left it on. That’s a ready-made discussion of systematic error. And because the sim is deterministic, every pair gets the same clean data, so weaker groups still reach a correct graph and the lesson time goes into interpretation rather than chasing anomalous readings — though you might deliberately ask pupils where real-lab scatter would come from, so they don’t leave thinking real data is this tidy.