The transformer sim
Build a step-up or step-down transformer from a demountable kit, read the voltages and currents into a table, and work out the turns ratio, the currents and the efficiency.
Electromagnetic induction: the transformer · covers the O-Level, IGCSE, GCSE (AQA: physics only, Higher tier only) topic
What the sim shows
A changing current in the primary coil makes a changing magnetic field. The soft-iron core carries it through the secondary coil, and the changing flux linkage induces an e.m.f. there (electromagnetic induction). For an ideal transformer Vp ÷ Vs = Np ÷ Ns, so more turns on the secondary step the voltage up and fewer step it down. No energy is lost, so VpIp = VsIs: stepping the voltage up steps the current down by the same factor. Real transformers lose energy (heating in the coils, and eddy currents and hysteresis in the core), so efficiency = VsIs ÷ VpIp × 100 % is below 100 %: this kit gives about 85–90 % with the yoke on, less at very low output. Without the yoke much of the flux leaks away at the gap instead of passing through the secondary, so Vs falls to about 40 %; with no iron core, to about 6 %. Direct current makes a steady field, and a field that is not changing induces nothing: the secondary only kicks when the current is switched on or off. Time is not stepped: each click is one action, and the needles take about 0.4 s to settle (the field view is slowed down; really 50 cycles a second). Model limits: the losses are lumped into two figures (10 % in the coils, plus a core loss that grows with Vp²); the primary current is treated as in step with the voltage, and the magnetising current a real core needs is left out, so with the lamp out Ip reads far smaller than on a real kit (a few milliamps instead of tens); the graph's best-fit line uses only rows taken with the same primary, supply, core and lamp; readings carry a seeded ±1 % meter scatter and are read to 3 significant figures; the secondary is kept below 25 V for safety, the 12 V lamp blows above 15 V and the supply cuts out above 8 A.
- Secondary voltmeter: Vs, the output voltage
- Coils of 120, 240, 600 and 1200 turns, two of each
- Laminated soft-iron core and yoke
Use it in your lessons
- Try it here: anyone can unlock 2 figures free, and a free account unlocks up to 5. Runs on a laptop, a Chromebook or a phone; nothing to install.
- Present it and share student links with the teacher plan, from US$5 a month, billed yearly.
- Put it on your own website or LMS for US$9, paid once, or every sim from US$29 a month.
Free guide: 12 practicals as sims, and how to run one in a lesson →
Need a version for your exact set-up? Have one made: US$49 a figure in an order of 5.
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