Table of Contents
Wireless Power Experiment Kids Can Do at Home
A wireless power experiment kids aged 11 and up can run on batteries: two coils, an LED, and a measurement that shows the energy only leaves when asked.
An LED glowing with no wires attached to it looks like a magic trick, which is exactly the problem. The useful version of this wireless power experiment kids can run at home is not the glowing LED. It is the multimeter wired into the transmitter. Bring the receiver coil close and the transmitter’s current climbs; take it away and the current drops back. The transmitter can tell the receiver is there, which means nothing was being broadcast into the room and then collected. Energy crossed the gap because something on the other side pulled on it. That single observation separates induction from the vague idea of beaming power through the air. Batteries only throughout. Nothing plugs into a wall.
Key Takeaways
- You’ll light an LED across an air gap of a centimetre or two using two coils, then measure how the gap, the alignment and the presence of a receiver change the transmitter’s current.
- It teaches inductive coupling, why coupling collapses with distance, and the difference between near-field magnetic coupling and radio.
- Best fit is ages 11 to 15. Below 11, the circuit work is frustrating even with help.
- The usual failure is expecting range. At this scale, the coils have to be within roughly one coil radius of each other. If your gap is bigger than the coil, nothing will happen.
- A coin or a foil wrapper left in the gap can get genuinely hot. Keep metal out, and keep the coils away from anyone with an implanted medical device.
What You’ll Need for a Wireless Power Experiment Kids Can Run
| Item | How much | Where to get it | If you don’t have it |
|---|---|---|---|
| Wireless power module pair, 5 V (transmitter + receiver boards with coils) | 1 set | Electronics shop or online, $4–8 | A hand-wound coil pair needs an oscillator circuit; the pre-built module is far more reliable |
| USB power bank | 1 | Already in the house | A 4×AA holder with a USB socket. Never a mains adapter |
| Multimeter with a mA and A range | 1 | Hardware shop, ~$12 | The headline measurement is impossible without it |
| Red LED, 5 mm | 2 | Electronics shop | A small buzzer |
| Enamelled copper wire, 0.3–0.5 mm | 5 m | Hobby shop, or unwind a dead motor | Any insulated thin wire, though thicker is harder to coil neatly |
| Cylindrical former, 5–7 cm across | 1 | A jar, a tape roll, a cardboard tube | Anything round and non-metallic |
| Non-metal ruler | 1 | School supplies | Marked card, which is better than a steel rule here |
| Assorted non-metal spacers (card, plastic lids, a book) | A few | Around the house | Sheets of paper, counted |
| Masking tape | 1 roll | Anywhere | Any tape |
Time: prep 20 min, experiment 35 min, cleanup 5 min Cost: $10–20 depending on what you own Mess level: low
Do the Experiment
Step 1 — Get the LED lit with no gap at all
Connect the transmitter board to the power bank. Solder or firmly twist the LED across the receiver coil’s two output pads. Lay the receiver coil directly on the transmitter coil, centres aligned.
What you should see: the LED lights. If it doesn’t, flip the receiver coil over, then flip the LED, then try the other LED. Get this working before you change anything else, because everything later is a comparison against it.
Step 2 — Measure the transmitter’s current with and without a receiver
Put the multimeter in series between the power bank and the transmitter, on a current range that can take at least 500 mA. Read the current with the receiver far away. Then slide the receiver coil into place and read it again.
What you should see: the current rises when the receiver arrives, often by a factor of two or more, and falls again when you remove it. Write both numbers down. This is the measurement that makes the whole topic make sense.
Step 3 — Walk the gap outwards, one spacer at a time
Stack card or plastic spacers between the coils and record LED brightness and transmitter current at each thickness. Measure each gap with the non-metal ruler. Go until the LED dies.
What you should see: brightness falls off far faster than the gap grows. Doubling the gap does not halve the output; it often kills it. With a 5 cm coil, expect useful transfer out to roughly 1 to 2 cm and nothing much beyond.
Step 4 — Slide sideways and tilt
Put the coils back in contact, then slide the receiver sideways in 5 mm steps while watching the LED. Return to centre, then tilt the receiver to 45° and then to 90°.
What you should see: a surprisingly sharp drop with sideways offset, and total extinction at 90°. A coil edge-on to the field lines catches almost nothing passing through it, which is the same reason a Qi phone charger wants your phone centred and flat.
Step 5 — Put metal in the gap, carefully
With an adult holding everything, slip a coin into the gap for no more than five seconds, then remove it and touch it briefly. Repeat with a piece of foil. Then try a plastic lid, a sheet of card and a book.
What you should see: the LED dims or dies with metal in the gap, and the coin is warm, sometimes alarmingly so. Plastic, card and paper do nothing at all: the field goes straight through them. That contrast is the clearest demonstration of why chargers tell you to remove cards and coins from a phone case.
What’s Actually Going On
The transmitter coil carries an alternating current, in the hundreds of kilohertz for a small module. That current produces a magnetic field whose direction reverses with every cycle. The receiver coil sits inside that changing field, and Faraday’s law of induction says a changing magnetic flux through a loop produces a voltage: EMF = -dΦ/dt. More turns, stronger field, faster change, more voltage. HyperPhysics sets out Faraday’s law formally, and the mechanism is identical to a transformer, with air where a transformer has an iron core.
The distance result from Step 3 is the whole engineering problem. On the axis of a circular loop of radius a, the field falls as 1/(a² + x²)^(3/2), which is almost flat while x is small compared with a and then collapses. The practical rule that comes out of that is unforgiving: separation much beyond the coil’s own radius and the coupling coefficient drops toward nothing. The Wireless Power Consortium’s Qi standard is built around exactly this constraint, which is why a phone charger is a pad you set the phone on rather than a box in the corner of the room.
There is a way to beat it, and the honest version is more interesting than the myth. In 2007, Kurs and colleagues at MIT published a scheme using two high-quality-factor resonators tuned to the same frequency, and transferred 60 watts across 2 metres at around 40 per cent efficiency using 60 cm diameter coils. The trick is that with high enough Q, even very weak coupling can move power efficiently, because energy sloshes back and forth many times before it is lost. Note the numbers, though: two metres with coils the size of a bicycle wheel. Scale matters, and nobody has beaten the physics since.
Now the correction that matters most. People describe wireless charging as beaming power through the air, as if the transmitter sprays energy outward and the receiver catches some of it. At these frequencies and distances the transmitter is not radiating usefully at all; it is a near-field magnetic source, and the receiver is magnetically linked to it the way two gear teeth are mechanically linked. Step 2 is the proof. If the transmitter were broadcasting, its current would not care whether a receiver existed. It does care, and dramatically.
The hot coin in Step 5 comes from eddy currents. A changing magnetic field drives circulating currents inside any conductor it passes through, and those currents dissipate as heat in the metal’s own resistance. It is the same effect an induction hob uses deliberately. On a charging pad it is purely a nuisance, and a thin foil wrapper trapped against a phone case is how people discover it.
How to Explain It to Your Kid
Ages 5–8: Two drums and a shared skin
Think of a drum and a second drum resting against it. Hit the first and the second buzzes, without anything passing between them except the push. Take them apart by a hand’s width and the second goes quiet. Let them move the coils closer and further and watch the light answer.
Then let them put a coin in. The light goes out and the coin gets warm, which is a surprising enough pair of facts to carry the whole idea at this age: the invisible thing is real, and it can go into metal.
Ages 9–12: The word is induction
Give them the word and one rule: a magnetic field that changes makes electricity in nearby wire, and a field that sits still does nothing. The second half explains why this needs alternating current and why a plain battery and coil would do nothing at all. Have them plot their own data from Step 3, gap against brightness, and label the point where it dies. Our walkthrough of shaking a magnet through a coil makes the same point with movement instead of frequency.
Ages 13+: Coupling, Q and why range is hard
Introduce the coupling coefficient k, the resonant frequency of an LC circuit, and the quality factor Q. Then set the design problem properly: transfer efficiency depends on the product k²Q₁Q₂, so you can trade poor coupling for high Q, which is precisely what the MIT resonant scheme did. The extension: wind two matched coils, add a capacitor to each to make them resonate at the same frequency, and compare their reach against the same coils without capacitors. Measuring the difference is a real afternoon’s work and a real result. For the circuit background on capacitors, see storing electricity and letting it go.
The question to ask: “If we made both coils twice as wide but kept the same number of turns, would the working gap get bigger or smaller?”
Why Teaching This Early Pays Off
The idea that a field can carry energy across empty space is one of the genuinely hard conceptual jumps in physics, and it arrives in secondary school as electromagnetic induction, usually in the form of equations. Having watched a transmitter’s current respond to a receiver’s arrival gives a student something concrete to attach those equations to, and it specifically pre-empts the “energy is a fluid in wires” model that makes induction feel impossible.
It also builds a usable scepticism about a kind of marketing claim children will meet constantly. Long-range wireless charging is announced every few years. Knowing that coupling collapses as roughly 1/distance³ beyond the coil radius, and that the serious research result is 60 watts across 2 metres with wheel-sized coils, is enough to evaluate those announcements without needing an engineering degree.
Keep the claims modest. One session does not change a trajectory, and the research does not support saying it does. What it does support is the value of the comparison structure used here. Chi and Wylie’s ICAP framework ranks constructing and defending explanations above merely doing, which means the plotting and the arguing about Step 2 carries the learning, not the glowing LED. The National Research Council’s K-12 framework names planning and carrying out investigations and using mathematics as two of its eight practices, and Steps 3 and 4 are both.
Before You Start: What Parents Should Know
| Best age | 11 and up. The circuit handling and the measurements both need patience that younger children reasonably do not have. |
| Supervision | Adult throughout. Adult-only for Step 5 and for any soldering. An adult should hold the coin with tongs or remove it quickly. |
| Real hazards | Eddy-current heating makes coins, foil, rings and keys hot enough to burn within seconds. Keep all metal out of the gap except for the brief, supervised test. Keep bank cards, transit cards and passports well away: the field can damage magnetic stripes and chips. Fine enamelled wire has sharp ends. |
| Don’t | Don’t run the transmitter from a mains adapter or a wall socket; use a power bank or a battery holder. Don’t bring the coils near anyone with a pacemaker, defibrillator or other implanted medical device; the FDA has specific guidance on magnets and implanted devices. Don’t try to “charge” a phone with a hand-wound coil. |
When It Doesn’t Work
- The LED never lights at zero gap. Work through it in order: LED polarity, receiver coil orientation, the LED itself, then the power bank. Many power banks shut down when they see a load under about 50 mA, which is a real and common cause. Try a different bank, or add a second LED in parallel to raise the draw.
- The LED lights but only in a tiny sweet spot. Your coils are mismatched in size. Coupling is best when the two coils have similar diameters; a small receiver over a large transmitter catches only part of the field.
- Brightness flickers wildly. Something metallic is near, often a steel ruler, a laptop or a radiator. Clear a 20 cm radius of metal and retest.
- The transmitter board gets hot. That’s normal within reason, since it is dissipating real power. If it becomes too hot to hold, disconnect it, check that no metal is bridging the coil, and let it cool.
- Your hand-wound coils do nothing. A plain coil on a battery produces a steady field, and a steady field induces nothing. You need something switching the current rapidly, which is what the module’s oscillator does. This is the single most common misunderstanding with homemade attempts.
Take It Further
Build the curve properly. Record transmitter current and LED brightness, using your phone’s camera in manual mode as a crude photometer, at 1 mm gap increments. Plot both against gap on the same axes. The point where current stops responding to the receiver is the coupling limit, and it is a sharper number than you’d expect.
Add resonance. Wind two identical coils, measure their inductance if your meter can, and add capacitors chosen so both resonate at the same frequency. Compare working range with and without. This is the Kurs experiment at kitchen scale, and the improvement is real and measurable.
Count the cost. Measure the transmitter’s input power and the receiver’s output power at zero gap and at 1 cm. The ratio is end-to-end efficiency. Commercial Qi charging typically lands in the 60 to 80 per cent range at best alignment, and your home-made version will be far worse. Finding out how much worse is the honest version of the experiment.
What to Watch For Over the Next 3 Months
- Week 4: they comment on why a phone has to be centred on a charging pad, or why a thick case stops it working.
- Month 2: the word induction turns up in a different context, often an induction hob or a metal detector.
- Month 3: they push back on a “charge your devices from across the room” claim and ask what size the coils are. That’s the win.
Frequently Asked Questions
Is the magnetic field from this harmful?
At these power levels and frequencies, exposure is comparable to a phone charging pad, which is a widely used consumer product. The documented risks are to implanted medical devices and to anything with a magnetic stripe or chip, not to healthy tissue. Keep the setup away from pacemakers and defibrillators, and follow the FDA’s guidance on magnets and implants.
Can we increase the range by using more turns or a bigger battery?
More turns helps a little, more voltage helps a little, and neither changes the geometry that dominates. Range scales with coil size. If you want more reach, make the coils bigger; that is what the MIT resonant demonstration did, and its coils were 60 cm across.
Why does a Qi charger not light our hand-wound coil?
Most Qi pads only switch on fully after a digital handshake with a certified receiver. Without that exchange they emit brief detection pulses, so you may see the LED blink rather than glow. It’s not a fault in your coil.
Can this charge a battery rather than light an LED?
Yes, if the receiver board includes a rectifier and regulator, which most 5 V modules do. Charge a battery holder with NiMH cells rather than anything lithium, and do not attempt to charge a phone or a lithium pack with a home-made supply.
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.
Sources
- Kurs, A., Karalis, A., Moffatt, R., Joannopoulos, J. D., Fisher, P., & Soljačić, M. (2007). “Wireless power transfer via strongly coupled magnetic resonances.” Science, 317(5834), 83–86. doi:10.1126/science.1143254
- Georgia State University. “Faraday’s Law.” HyperPhysics. http://hyperphysics.phy-astr.gsu.edu/hbase/electric/farlaw.html
- Wireless Power Consortium. “Qi.” https://www.wirelesspowerconsortium.com/qi/
- U.S. Food and Drug Administration. “Magnets in Cell Phones and Smart Watches May Affect Pacemakers and Other Implanted Medical Devices.” https://www.fda.gov/radiation-emitting-products/cell-phones/magnets-cell-phones-and-smart-watches-may-affect-pacemakers-and-other-implanted-medical-devices
- Chi, M. T. H., & Wylie, R. (2014). “The ICAP framework: Linking cognitive engagement to active learning outcomes.” Educational Psychologist, 49(4), 219–243. doi:10.1080/00461520.2014.965823
- National Research Council. (2012). A Framework for K-12 Science Education. National Academies Press. doi:10.17226/13165
- Occupational Safety and Health Administration. (2002, revised). Controlling Electrical Hazards, OSHA Publication 3075. https://www.osha.gov/sites/default/files/publications/osha3075.pdf
- National Capital Poison Center. “Swallowed a button battery?” Poison Control. https://www.poison.org/battery
