Faraday Induction Experiment: Shake a Magnet, Light an LED

Hold the magnet still inside the coil and nothing happens. That is the sentence this whole build exists to produce, because it kills the idea that magnets contain electricity waiting to be let out. A Faraday induction experiment done properly makes electricity out of motion and only out of motion, and the two LEDs wired back to back give it away: one flashes as the magnet goes in, the other as it comes out. Be warned, this is the most finicky experiment in this collection, and the difference between a result and a disappointment is almost entirely the number of turns on your coil.

Key Takeaways

• You’ll wind around 500 turns of fine enamelled wire on a clear tube and shake a magnet through it to flash two LEDs.
• It teaches electromagnetic induction: a changing magnetic field through a coil drives a current, and a steady one does not.
• Best from about age 10, with an adult managing the magnet and the fine wire.
• What usually goes wrong: too few turns. At 200 turns you need a multimeter to see anything; at 500 you get a visible flash in a dark room.
• The honest version of this result is dim. Say so in advance, and have the multimeter fallback ready.

What You’ll Need

Item	How much	Where to get it	If you don’t have it
Clear plastic tube	One, 12–16 mm inside diameter, 12–15 cm long	An effervescent vitamin tube, a clear pen barrel with the ends cut off	A rolled sheet of acetate taped into a tube
Enamelled copper wire	40–60 m, 30 AWG (0.25 mm)	Motor rewinding shop, electronics shop	Salvage from a transformer or a stepper motor
Neodymium magnet	One, 10–12 mm diameter, that slides freely in the tube	Hardware shop, or a dead hard drive	Two thin discs stacked. Ferrite will not work
LEDs	2, red, 5 mm	Electronics shop, or salvage	Two of any colour, but red lights at the lowest voltage
Digital multimeter	One	Hardware store	None. This is the fallback when the LEDs refuse
Sandpaper, tape, foam earplugs	A little of each	Toolbox and bathroom	Earplugs or cotton wool cap the tube ends
A dark room	One	Close the curtains	—

Time: prep 45 min, mostly winding; experiment 25 min; cleanup 5 min Cost: around 10 to 15 dollars for wire, magnet and LEDs Mess level: low

Do the Experiment: Build the Faraday Induction Experiment

Step 1 — Wind the coil, and wind more than you think

Leave 20 cm of wire free, then wind tightly in one direction in a band 3 to 4 cm wide in the middle of the tube, layer on layer, counting in blocks of fifty. Aim for 500 turns. Tape each layer so nothing springs loose, leave another 20 cm free at the end, and sand both wire ends until bright pink.

This takes half an hour and it is the whole experiment. A 200-turn coil will not light an LED, and no amount of shaking will fix that.

Step 2 — Wire two LEDs back to back across the coil

Twist the two coil ends to the two LEDs connected in opposite directions: the long leg of one to the short leg of the other, at both junctions. The pair is now antiparallel, so whichever way the current flows, one of them can conduct.

Step 3 — Predict three things, then test them one by one

Will the LED light if the magnet sits still inside the coil? If it moves slowly? If it moves fast? Get three separate answers out loud, because the three results are what the mechanism is made of.

Step 4 — Hold the magnet still inside the coil

Push it into the middle and stop.

What you should see: nothing at all, indefinitely. A strong magnet sitting inside 500 turns of copper produces no current whatsoever, which is the result that matters most in this article.

Step 5 — Drop the magnet through, then shake hard, in the dark

Cap one end with a foam earplug so the magnet cannot fly out, switch the lights off, let eyes adjust for thirty seconds, then shake the tube hard along its axis.

What you should see: short flashes, alternating between the two LEDs. On a slow drop you may see one weak flicker per LED. On hard fast shaking you get a stuttering alternation. It is dim. In full daylight you will see nothing at all, which is why the dark room is in the materials list.

Step 6 — Switch to the multimeter and get numbers

Disconnect the LEDs, set the meter to its lowest AC volts range, and clip it across the coil. Shake slowly, then fast.

What you should see: tens of millivolts for slow motion, hundreds for vigorous shaking, with a clear and repeatable difference between the two. This is the version that always works, and for a child who likes numbers it is more convincing than the flash.

What’s Actually Going On

Michael Faraday established the principle in 1831 and published it the following year: moving a magnet relative to a loop of wire produces a current in the wire, and what matters is the rate of change rather than the strength of the field itself (Faraday, 1832). The modern statement is that the voltage induced round a loop equals the rate of change of magnetic flux through it, and for a coil of many turns the contributions add, so the voltage is multiplied by the number of turns (HyperPhysics, Georgia State University).

Both halves of that sentence are visible in your tube. Rate of change is why a stationary magnet does nothing: the flux through the coil is large but constant, so its rate of change is zero, so the voltage is zero. It is also why shaking harder works better. And the number of turns is why 500 beats 200 by more than you would guess, since you are multiplying the whole effect by N.

The two LEDs reveal something subtler. As the magnet enters, flux through the coil is increasing. As it leaves, flux is decreasing. The induced voltage therefore reverses sign, and current flows one way then the other. That is alternating current, generated by a hand, with the direction change made visible by two diodes that each conduct only one way. Every power station on Earth works on this principle, with rotation instead of shaking, and understanding that the reversal is intrinsic rather than a design choice is a genuine insight.

There is a third effect you can feel. The induced current itself creates a magnetic field, and that field always opposes the change that produced it. This is Lenz’s law, and the consequence is that the magnet is slightly resisted on its way through the coil. With LEDs connected the effect is tiny, because they block current below their forward voltage. Short the coil ends together instead and drop the magnet through, and the fall is measurably slower. It is the same braking that makes a magnet crawl down a copper pipe.

Now the honest part about brightness. A red LED needs roughly 1.8 volts before it conducts at all, which follows from the photon energy it has to supply, about 1.77 electronvolts at the red end of the spectrum (HyperPhysics, LEDs). Your coil produces that only during the fast part of the magnet’s passage, in bursts lasting a few tens of milliseconds. So the light is a flicker, not a glow, and blue or white LEDs needing nearer 3 volts usually stay dark. A commercial shake torch solves this with thousands of turns, a heavier magnet and a capacitor to smooth the output. Knowing why your version is dimmer than the shop-bought one is more educational than owning the shop-bought one.

How to Explain It to Your Kid

Ages 5–8: Moving makes the electricity

A magnet sitting still is just a magnet. A magnet that moves past a coil of wire pushes the electricity inside the wire along, a bit like waving your hand in a bath makes the water move. Stop waving and the water stops. Have them hold the magnet still in the tube and see nothing, then shake it and see the little flashes. Then let them try to make it light by shaking gently, which will not work, so they discover for themselves that speed is the thing.

Ages 9–12: Rate of change, and why there are two LEDs

Introduce the key word: it is not the magnetic field that makes the current, it is the change in the magnetic field. Then the two-LED puzzle. Ask why there are two and why they take turns rather than lighting together. The answer, that going in and coming out push the current in opposite directions, is the definition of alternating current, and they can work it out from what they just watched.

Ages 13+: Faraday’s law, quantitatively, and Lenz

Give them the law as voltage equals turns multiplied by the rate of change of flux, then design the experiment that tests the N dependence. Wind a second coil of 250 turns on an identical tube and compare peak millivolts at matched shaking speeds. The ratio should be close to two. Research on university students found that electromagnetic induction is one of the topics where learners most often substitute a vague association for the actual causal relationship (Guisasola, Almudí & Zuza, 2013), so insisting on the rate-of-change wording rather than “magnets make electricity” is doing real work.

The question to ask: “If I keep the magnet still and move the coil instead, does anything happen?”

Why Teaching This Early Pays Off

Induction is the invisible foundation of modern civilisation and almost nobody can explain it. Every watt from a power station, every wireless charger, every transformer on a telegraph pole, every electric guitar pickup, every induction hob and every regenerative brake runs on the relationship your child just shook into a plastic tube. It is also the reverse of the motor effect, so once a child has done both, electricity and motion become two directions of one road rather than two subjects.

The specific intellectual gain is the concept of a rate of change as a cause. Most children’s causal reasoning is about states: this is hot, that is strong, this is heavy. Induction cannot be explained in those terms at all, because a strong field causes nothing and a changing weak one causes something. Meeting that idea in a physical object at ten or twelve makes calculus, when it arrives, look like notation for something already familiar. No single evening does that on its own. But a child who has held a magnet still inside a coil and seen nothing happen has an anchor that a textbook diagram cannot provide.

Before You Start: What Parents Should Know

Best age	10 and up. The winding is tedious and needs patience, and an adult should expect to do some of it
Supervision	Adult manages the neodymium magnet and the fine wire. Children wind, count and shake
Real hazards	The magnet is the hazard, not the electricity. Neodymium discs snap together hard enough to pinch and to chip into sharp fragments, they wipe bank cards and interfere with pacemakers, and two or more swallowed magnets attract through tissue and often require surgery, as the US Consumer Product Safety Commission sets out. Cap both ends of the tube so the magnet cannot launch out during hard shaking
Don’t	Don’t connect this coil to anything mains-powered to “test” it, and don’t substitute a mains transformer as a shortcut. The whole point is that this circuit generates its own few hundred millivolts and has no external supply at all. Also don’t let two magnets approach each other at speed: they collide hard enough to shatter and send fragments toward eyes

When It Doesn’t Work

• The LEDs never light, even in the dark. Almost always too few turns. Count what you actually wound rather than what you intended. Below about 400 turns on a tube this size, the voltage rarely clears an LED’s forward threshold, and the fix is more wire rather than more effort.
• The multimeter shows millivolts but the LEDs stay dark. This is consistent and expected. Your coil is producing voltage, just not enough of it. Add turns, use a stronger or heavier magnet, or accept the multimeter as the output device.
• Nothing reads at all. Check the wire ends. Enamel is invisible and unsanded ends mean an open circuit. Measure continuity across the coil first: a 500-turn coil of 30 AWG should read somewhere in the tens of ohms, and an open circuit reads infinite.
• The magnet sticks inside the tube. Something ferrous is nearby, or the tube is too tight. The magnet should slide freely under gravity when the coil is disconnected. If it jams, use a slightly smaller magnet.
• One LED flashes and the other never does. Check the antiparallel wiring: both junctions need one long leg joined to one short leg. If they are parallel rather than antiparallel, only one direction of current can flow.

Take It Further

Turns versus voltage: wind 250 turns on one tube and 500 on another, identical in every other respect. Record peak millivolts for a drop from a fixed height, five trials each. The ratio should land near two, and measuring how close it gets is a genuine test of Faraday’s law rather than an illustration of it.

Speed versus voltage: drop the same magnet through the same coil from heights of 10, 20, 30 and 40 cm, recording peak voltage. Speed at the coil goes as the square root of the drop height, and voltage goes with speed, so the graph of voltage against height should curve rather than run straight. Predicting that curve before plotting it is the exercise.

Where This Faraday Induction Experiment Belongs in a Sequence

Do the forward direction first. Winding a nail into an electromagnet shows current producing magnetism, and this experiment is that relationship run backwards, so having both makes each one clearer. The natural partner is dropping a magnet down a copper pipe, which is the same induced current seen as a braking force instead of as a voltage, and the two together give you Lenz’s law from two angles. Afterwards, building a hand-crank generator from a motor replaces shaking with rotation and finally produces enough power to be useful. If the LED side of this was the frustrating part, how LEDs actually work explains the forward-voltage threshold you ran into.

What to Watch For Over the Next 3 Months

• Week 4: they use the word “changing” unprompted when talking about magnets and electricity, rather than just “strong”.
• Month 2: they work out, or ask, how a wireless phone charger manages it without any contact.
• Month 3: they connect the alternating part to why household electricity is called AC, which is a leap worth encouraging.

Frequently Asked Questions

Why does nothing happen when the magnet sits still?

Because induction depends on the rate of change of magnetic flux, not on the amount of flux. A stationary magnet produces a large but constant field through the coil, so the rate of change is zero and so is the voltage. This is the single most important observation in the experiment.

How many turns do I really need?

Around 500 for a visible LED flash on a 12 to 16 mm tube with a 10 to 12 mm neodymium magnet, in a dark room. At 200 turns you will measure voltage on a multimeter but see no light. Voltage scales with the number of turns, so adding wire is always the most effective fix.

Why two LEDs instead of one?

Because the induced voltage reverses as the magnet goes in and then out. An LED conducts in only one direction, so a single one would light on only half the passes. Wiring two in opposite directions makes the reversal visible, which is the point.

Can I use any magnet?

It has to be neodymium. Ferrite and fridge magnets produce a field one or more orders of magnitude weaker, and since the voltage follows the field’s rate of change, a weak magnet gives a weak result no matter how hard you shake it.

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About the author

Ricky Flores is the founder of HiWave Makers and an electrical engineer with 15+ years of experience building consumer technology at Apple, Samsung, and Texas Instruments. He writes about how kids learn to build, think, and create in a tech-saturated world. Read more at hiwavemakers.com.

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Sources

1. Faraday, M. (1832). “Experimental researches in electricity.” Philosophical Transactions of the Royal Society of London, 125–162. https://doi.org/10.1098/rstl.1832.0006
2. Nave, R. “Faraday’s Law.” HyperPhysics, Georgia State University. http://hyperphysics.phy-astr.gsu.edu/hbase/electric/farlaw.html
3. Nave, R. “Light Emitting Diodes.” HyperPhysics, Georgia State University. http://hyperphysics.phy-astr.gsu.edu/hbase/electronic/led.html
4. Guisasola, J., Almudí, J. M., & Zuza, K. (2013). “University Students’ Understanding of Electromagnetic Induction.” International Journal of Science Education, 35(16), 2692–2717. https://doi.org/10.1080/09500693.2011.624134
5. U.S. Consumer Product Safety Commission. “Magnets.” https://www.cpsc.gov/Safety-Education/Safety-Education-Centers/Magnets
6. National Research Council. (2012). A Framework for K-12 Science Education. National Academies Press. https://doi.org/10.17226/13165