How Wireless Charging Works: Faraday's 1831 Discovery in Your Phone

Your kid sets their phone on a flat pad on the nightstand. No plug. No cable hunting. Two seconds later, the charging icon appears on the screen. They barely notice.

What just happened is one of the most fundamental phenomena in physics — electromagnetic induction. The same discovery that Michael Faraday made in 1831 when he moved a magnet through a coil of wire and watched a current appear in that wire. The same principle that makes generators at power plants convert rotating motion to electricity. The same principle that lets transformers step voltage up or down on the electrical grid.

The wireless charging pad on your nightstand and the massive generators at Niagara Falls are running on the same physics. That’s worth knowing.

The Core Problem: “Wireless” Sounds Like Magic

When something is wireless, we tend to stop asking how it works. WiFi is wireless. Bluetooth is wireless. Wireless charging is wireless. They must all be similar, right?

Not really. WiFi and Bluetooth use electromagnetic waves — they transmit energy as radio waves that propagate through space at the speed of light over long distances. Wireless charging works completely differently: it uses a direct magnetic coupling between two coils that must be physically close together (usually within a few millimeters). It’s not broadcasting energy through the air like a radio station. It’s more like a transformer — two coils of wire coupled magnetically, transferring power from one to the other.

This distinction matters because it explains why wireless charging only works when the phone is sitting right on the pad, not from a foot away.

Explained Like You’re 5: The Invisible Magnetic Bridge

Imagine you have two rings made of wire, and you put one inside the other. You push electricity through the inner ring. That flowing electricity creates a magnetic field around it — like an invisible force bubble. Now, if that magnetic field is changing (getting stronger or weaker), it can reach out and push electricity into the outer ring, even without touching it.

That’s electromagnetic induction. The charging pad has the inner ring (called a transmitter coil). Your phone has the outer ring (called a receiver coil). The pad’s coil creates a changing magnetic field. Your phone’s coil catches that changing field and converts it back to electricity.

No wires between them. Just a shared magnetic field.

How It Actually Works: The Qi Standard and Resonant Coupling

The Basic Components

Every wireless charging system has two halves:

The transmitter (charging pad): An alternating current (AC) runs through a flat spiral coil inside the pad. Because the current alternates — switches direction — rapidly (typically at 100–200 kHz), the magnetic field it creates alternates rapidly too. This alternating magnetic field extends a short distance above the pad’s surface.

The receiver (inside the phone): Another flat spiral coil is embedded just behind the phone’s back panel. When this coil is placed in the alternating magnetic field from the pad, Faraday’s law of induction causes a current to flow in it. This alternating current is then converted to direct current (DC) by a rectifier circuit inside the phone and used to charge the battery.

The Qi Standard Qi (pronounced “chee,” from the Chinese concept of life force or energy flow) is the dominant wireless charging standard, managed by the Wireless Power Consortium. It was released in 2008 and is now built into billions of devices. Qi specifies the frequency range, coil geometries, communication protocol (the transmitter and receiver actually communicate over a Bluetooth-like channel to coordinate charging speed), and safety requirements.

Most iPhones since iPhone 8 and most Android flagships support Qi at 5–15W.

MagSafe and Qi2 Apple’s MagSafe (introduced with iPhone 12 in 2020) added a ring of magnets around the iPhone’s internal charging coil to ensure precise alignment with the charging pad. Perfect alignment is critical for efficiency — misaligned coils transfer power less efficiently and generate more heat. MagSafe achieves 15W charging because the alignment is reliable.

Qi2 (released in 2023) adopted Apple’s MagSafe magnet alignment system as an open standard, extending 15W wireless charging to all compatible Android devices.

Why Kids Should Know This

Electromagnetic induction is one of the most consequential physics discoveries in human history. Faraday’s 1831 experiments led directly to:

• The electric generator (coils rotating in a magnetic field to produce AC electricity)
• The electric motor (the reverse: AC electricity in coils creating rotation)
• The transformer (coils coupled magnetically to step voltage up or down)
• Induction cooktops (eddy currents induced in the bottom of a metal pan generate heat directly in the pan)
• Transcranial magnetic stimulation (medical devices that induce currents in brain tissue to treat depression)
• Wireless EV charging systems being deployed at some highway rest stops
• The principle behind every MRI machine (though that’s a more complex story)

A kid who understands that “a changing magnetic field creates a current in a nearby conductor” has a conceptual key that unlocks most of electrical engineering. This isn’t a niche topic — it’s the organizing principle of how civilization generates and distributes power.

The paper circuits project on this site explores how circuits carry current, which is the foundation for understanding both sides of the induction relationship.

How to Teach Your Kid About This

Ages 5–8: The Invisible Push

You’ll need: a small bar magnet, a compass, and optionally a coil of wire and a galvanometer (or even a basic LED).

Hold the magnet still near the compass — the needle points toward the magnet. Now move the magnet back and forth rapidly. Watch the needle swing. Ask: “What’s making the needle move?” (The changing magnetic field.)

If you have a coil and galvanometer: slowly move the magnet through the coil. The meter needle deflects slightly. Move it fast — the needle deflects more. Stop — the meter drops to zero. Ask: “What’s different between when I move it slowly and when I stop?” (The changing field creates current; a stopped magnet creates no current.)

This is Faraday’s law of induction, demonstrated in your kitchen.

Ages 9–12: Efficiency Measurement

You’ll need: a USB power meter ($10–$15 online), a wireless charging pad, and your phone.

Measure: plug the wireless charging pad into a USB power meter. Charge your phone wirelessly. Record the wattage the pad draws. Now charge with a cable and record that wattage too.

Wireless charging typically draws 15–25% more power from the wall than equivalent wired charging, because the coil coupling isn’t perfectly efficient — some energy is lost as heat. Calculate the efficiency: efficiency (%) = (wired charging power / wireless charging power) × 100.

Ask: “Over a year of daily charging, how much extra energy does wireless charging use compared to wired?” Run the math. Then: “Is that worth the convenience to you?”

Ages 13+: Resonant Coupling and Distance

Standard Qi charging works at a few millimeters distance. But there’s a related technology called resonant inductive coupling that works over larger distances — the basis for some wireless EV charging systems and the research goal of mid-range wireless power transfer.

Research: MIT’s 2007 demonstration of “WiTricity” transferred 60W of power wirelessly over about 2 meters with 40% efficiency using resonant coupling. How does tuning two coils to the same resonant frequency improve range compared to basic Qi coupling?

Advanced project: Build a simple wireless power transfer demonstration. You need two 10-turn coils of enameled copper wire, a 555 timer circuit (or an Arduino) to create an oscillating signal in the transmitter coil, and an LED connected to the receiver coil. When the coils are aligned, the LED lights up without a direct connection. This is a buildable, educational project using about $15 in components.

Safety note: Wireless charging generates heat in both the pad and the phone. This is normal and safe at standard power levels. Avoid leaving phones on wireless chargers in hot cars or under pillows, where heat cannot dissipate. Do not use damaged or non-certified wireless chargers.

Wireless Charging Standards Comparison

Standard	Max Power	Coil Alignment	Range	Heat Generation	Device Compatibility	Notes
Qi (baseline)	5–15W depending on device	Free placement (some drift OK)	0–5mm	Moderate	Universal — most smartphones	Original standard; widely supported
MagSafe (Apple)	15W (iPhone 12+)	Magnetic snap alignment	0–5mm	Low (alignment efficiency)	iPhone 12 and later	Proprietary magnet ring; fastest for iPhone
Qi2	15W	Magnetic snap alignment (MagSafe-compatible)	0–5mm	Low	iPhones + Android (Qi2 certified)	Open standard version of MagSafe; 2023+
Proprietary fast wireless (Samsung, OPPO, etc.)	25–65W	Pad-specific alignment	0–5mm	Higher	Brand-specific devices only	Faster but requires brand-matched hardware
Resonant (WiTricity/SAE J2954 for EVs)	Up to 11kW	Approximate alignment (±10cm)	Up to 25cm	Moderate	EVs with compatible receivers	Long-range; EV charging focus

Common Misconceptions Parents Have

“Wireless charging is completely safe but slower — might as well use a cable.” The safety part is true; the “slower” part is increasingly outdated. Qi2-certified chargers deliver 15W to compatible phones — essentially identical to standard wired charging on most phones. High-wattage fast charging (30W+) still requires a cable, but for overnight charging or typical use, modern wireless charging speed is adequate.

“Wireless charging works through phone cases.” Generally yes, with thin cases. Most plastic and leather cases under about 3mm thick don’t significantly impede the magnetic field. Thick cases, or cases with metal plates (like some wallet cases) can block or significantly reduce wireless charging. Cases with metal credit card holders often block it entirely.

“Wireless charging will damage my battery faster.” Wireless charging does generate slightly more heat than wired, and heat is the primary driver of lithium-ion battery degradation. Overnight wireless charging in a case that traps heat could incrementally affect long-term battery health. For most people and typical use, the difference is minor. For maximum battery longevity, charge to 80%, avoid extreme temperatures, and occasional wired charging is fine.

“All wireless chargers are the same.” No. Cheap, uncertified wireless chargers may not properly regulate power, may run hot, and lack the safety features (foreign object detection, overcharge protection) required by the Qi standard. Look for Qi-certified chargers — the Wireless Power Consortium maintains a certification database.

“Wireless charging works from any distance.” Standard Qi requires physical contact or near-contact (under ~5mm). The “wireless” refers to the absence of a cable, not distance charging. True over-the-air power delivery at meaningful distances remains in research/development and is not commercially available for consumer electronics.

What to Watch For: Progress Markers

Your child understands the basics when they can explain why the phone must be touching (or nearly touching) the pad — and connect this to the fact that the magnetic field weakens rapidly with distance.

They’ve gotten deeper when they can explain the role of the alternating current — why the magnetic field must be changing (not static) to induce a current in the receiver coil.

At the advanced level, look for them to make the connection to power generators: “So the generator at a power plant is also running on Faraday’s law? It’s just coils spinning in a magnetic field?” Yes. The same equation, a different geometry.

FAQ

Q: Can wireless charging damage my phone? A: Not under normal circumstances with certified chargers. The Qi standard includes extensive safety protocols: foreign object detection (to avoid heating metal objects on the pad), temperature monitoring, and overcharge protection. Use Qi-certified chargers and the risk of damage is extremely low.

Q: Why does my phone sometimes feel warm after wireless charging? A: Inductive coupling isn’t 100% efficient. Some energy is lost as heat — in the pad, in the phone’s receiver coil, and in the phone’s battery itself. This is normal. If the phone gets uncomfortably hot (above ~40°C/104°F), remove it from the charger, remove the case if you’re using one, and let it cool before continuing.

Q: Will wireless charging work through a thick phone case? A: Thin cases (plastic, silicone, leather under ~3mm) generally work fine. Thick cases, metal cases, wallet cases with metal plates, or cases with NFC-blocking material often interfere. If charging seems slow or inconsistent, try removing the case.

Q: Can I leave my phone on a wireless charger all night? A: Modern iPhones and Android flagships have overcharge protection — they stop charging at 100% and resume when the battery drops slightly. Some have “optimized charging” features that learn your schedule and delay charging to 100% until shortly before you typically wake up, reducing time at full charge. This extends battery longevity. Using these features, overnight wireless charging is fine.

Q: Are there wireless chargers that work at distances greater than a few millimeters? A: Not for consumer electronics yet. Resonant inductive coupling (used in some wireless EV charging systems) works over 10–25 cm, and researchers have demonstrated even longer ranges at low power — but commercial products for charging phones at a distance haven’t reached market. Ultrasound and RF-based power transfer are in development but remain niche and low-efficiency.

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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. Wireless Power Consortium. “Qi Specification.” https://www.wirelesspowerconsortium.com/developers/specification.html
2. Kurs, A., et al. (2007). “Wireless Power Transfer via Strongly Coupled Magnetic Resonances.” Science, 317(5834), 83–86.
3. Apple. “MagSafe Charger Technical Specifications.” https://support.apple.com/en-us/111900
4. IEEE Standards Association. “IEEE 802.11 and Wireless Charging Coexistence.” https://standards.ieee.org
5. Faraday, M. (1831). “Experimental Researches in Electricity.” Philosophical Transactions of the Royal Society.
6. U.S. Department of Energy. “Electric Vehicle Charging.” https://www.energy.gov/eere/electricvehicles/charging-home