The Transformer: Changing Voltage with Electromagnetic Induction
Simulation Description
This simulation models a basic transformer as specified in AQA GCSE Physics Paper 2 (Magnetism and Electromagnetism). It shows a laminated E-I core with two coils wound around the left and right limbs, rendered in high-quality 3D with physically based materials — steel-blue laminated iron core with visible lamination lines, and sharp copper-coloured wire turns that students can count directly from the screen.
The physics runs live at every frame. An AC input is applied to the primary coil (left limb, amber current arrows). The alternating current creates a continuously changing magnetic flux that circulates around the closed iron core, shown as blue arrows travelling up the left limb, across the top yoke, down the right limb, and back along the bottom — the complete magnetic circuit. The flux arrows reverse direction every half-cycle as the AC reverses. Because the flux is always changing, it induces an EMF in the secondary coil (right limb, purple current arrows) by Faraday’s law. The secondary current opposes the primary’s flux change in accordance with Lenz’s law, so the secondary arrows always run counter to the primary.
The dual waveform display (top-left, always visible) shows the primary (amber) and secondary (purple) voltage waveforms. Both are the same frequency — reinforcing that a transformer does not change frequency, only voltage. The secondary waveform is drawn to scale: for a step-up transformer the purple trace is visibly taller than the amber trace; for a step-down transformer it is shorter. Students can see the amplitude ratio directly without needing to do a calculation first.
The equation card (top-right, always visible) shows Vs/Vp = Ns/Np in live numbers that update with every slider movement. The step-up/step-down/isolation label updates automatically. Students can manipulate four sliders in the bottom strip: Vp (input voltage, from 12 V to 1000 V including real-world values like 230 V mains and 400 V three-phase), Np (primary turns 2–12), Ns (secondary turns 2–12), and AC frequency (10–80 Hz). Dragging the scene to any angle reveals the coil windings on each limb, the core geometry, and the flux arrows within the core.
The 🏷 Labels button adds the five-step GCSE causal chain: AC in primary coil → changing flux in iron core → flux links secondary coil → EMF induced (Faraday) → Vs/Vp = Ns/Np.
Suggested Class Activity
“Design the Transformer” — Turns Ratio Investigation Suitable for: GCSE Physics Year 10/11 — Transformers lesson. 25–30 minutes.
Setup (2 min) Display the simulation with Np = 4, Ns = 8, Vp = 230 V, labels off. Students have a printed results table or mini whiteboard.
Stage 1 — Establish the rule (5 min) Point to the equation card. Ask: “The input is 230 V. The output shows 460 V. The primary has 4 turns and the secondary has 8. What do you notice about the ratio of turns and the ratio of voltages?” Target: Ns/Np = 8/4 = 2, and Vs/Vp = 460/230 = 2. They are equal.
Ask: “What do we call a transformer where the output voltage is higher than the input?” Target: step-up transformer.
Stage 2 — Prediction challenge (6 min) Students predict the output voltage before touching the sliders for each of the following:
| Vp | Np | Ns | Predicted Vs | Actual Vs |
|---|---|---|---|---|
| 230 V | 4 | 8 | ? | |
| 230 V | 8 | 4 | ? | |
| 230 V | 4 | 4 | ? | |
| 100 V | 2 | 10 | ? | |
| 12 V | 3 | 12 | ? |
After each prediction, set the sliders and check the equation card. Students note whether the waveform strip confirms their answer visually.
Stage 3 — Waveform comparison (4 min) Ask students to watch both waveforms as they move from Ns = 2 to Ns = 12 (keeping Np = 4, Vp = 230 V). Ask: “What stays the same about the two waveforms no matter what you do with the sliders?” Target: the frequency is always identical — both traces complete cycles at the same rate. A transformer cannot change the frequency of the AC supply.
Stage 4 — Real-world contexts (5 min) Set Vp = 230 V (UK mains). Ask students to find the turns ratio needed for:
- Charging a phone at 5 V — Ns/Np = 5/230 ≈ 0.022 (step-down, many fewer secondary turns)
- National Grid transmission at 400,000 V — Ns/Np = 400,000/230 ≈ 1739 (step-up, many more secondary turns)
Students don’t need to hit exact values on the slider — the point is the direction and magnitude of the ratio, and what it means physically.
Toggle 🏷 Labels on and connect the step chain to the real-world examples: why does the National Grid use step-up transformers? And why are step-down transformers needed at the consumer end?
Stage 5 — Written explanation (5 min) Students write a GCSE mark-scheme answer to: “Explain how a transformer steps up the voltage from 230 V to 2300 V, and state what turns ratio is needed.”
Use the step chips as a writing frame. A strong answer will include: AC in primary → changing flux in iron core → flux links secondary → EMF induced by Faraday’s law → Vs/Vp = Ns/Np → ratio = 10:1 so Ns = 10 × Np.
Adaptation notes
- For lower-confidence learners: leave labels on throughout; use the equation card numbers as a worked example before predictions; start with 1:1 isolation transformer to establish baseline
- For higher ability: ask why the transformer only works with AC and not DC; link to the flux arrows — DC would produce a constant flux with no change, so dΦ/dt = 0 and no EMF is induced in the secondary
- For SEND learners: extra-slow mode in the accessibility panel; the reading ruler supports the equation card; the waveform height difference is a visual analogy that works without reading any numbers