The a.c. generator and d.c. dynamo sim
Turn a coil between magnet poles, read the peak e.m.f. and period from an oscilloscope, work out the frequency, then swap in a commutator for d.c. (dynamo mode, AQA only) and load it with a lamp.
Electromagnetic induction · covers the O-Level, IGCSE, GCSE topic
What the sim shows
Turning the coil makes its long sides cut the magnetic field lines, and this induces an e.m.f. The e.m.f. is biggest when the coil's plane lies along the field (90° and 270°: the sides cut the lines fastest) and zero when the plane is at right angles to the field (0° and 180°: for that instant the sides move along the lines). Slip rings keep each end of the coil joined to the same brush, so the output reverses every half turn: alternating current, a sine wave on the oscilloscope. Read the peak from the centre line (divisions × VOLTS/DIV) and the period of one whole wave (divisions × TIME/DIV), then work out the frequency, f = 1 ÷ T. Turn faster and the peak gets bigger and the frequency higher: double the speed and both double. With Labels on, blue field lines run from N to S and orange arrows on the coil's long sides show the induced current (Fleming's right-hand rule); the end view under the drawing shows the same coil seen along its axle, with ⊙ for current towards you and ⊗ for current away. Swap the slip rings for a split-ring commutator and the coil's ends change brushes every half turn, just as its e.m.f. reverses, so the output never reverses: d.c. that varies but keeps one direction. The coil's own e.m.f. still reverses, so the readout gives it a sign; only the output is one way round. When the lamp takes current, the crank is harder to turn (the turning effort bar grows), because energy is needed to make the current. Model and limits: the field between the flat poles is taken as uniform; the coil has 2 Ω of resistance, so with the 6 Ω lamp the output is three-quarters of the e.m.f.; this small generator gives at most 1.3 V, so the 1.5 V lamp only glows dull orange even at 10 turns a second; the trace has a width, so your readings scatter a little. Time runs in real time and Pause stops it; a coil held still gives no e.m.f., so a paused reading belongs to that instant of a steady turn. Above 3 turns a second the coil is blurred in the drawing, but the trace and the readings stay in real time.
- Crank handle: drag it round (mouse or finger), or press Turn steadily
- Coil: 100 turns, 4.0 cm × 5.0 cm, turning between N and S
- Oscilloscope trace: output p.d. against time
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 →
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