# How does an induction stove heat a pan?

> There's no flame and no glowing ring. A copper coil under the glass makes the bottom of your pan act like the wire in a toaster.

https://learnfold.app/wait-how/how-induction-cooktops-work/ · Updated 2026-11-03

An induction stove doesn't make a flame or heat a glowing ring. Under the glass sits a flat coil of copper wire. Alternating current runs back and forth through it tens of thousands of times a second, and that makes a magnetic field that flips just as fast. The field passes through the glass and into the base of a magnetic steel or iron pan, where it drives loops of electric current. The metal resists those currents, and that resistance turns them into heat. So the pan heats itself. The glass only gets warm because the hot pan is sitting on it.

## Under the glass is a coil, not a burner

An application note from the chipmaker onsemi describes the layout. A coil of copper wire sits underneath the cooking pot, with a layer of ferrite under the coil in its diagram. An alternating current flows through the coil, "which produces an oscillating magnetic field."

Alternating means it flips direction, over and over. In one design in the onsemi note, the current switches between about 24,700 and 45,000 times a second, depending on the power setting. The surprise is which way round it goes. That design runs at 45 kHz for 1,200 watts and drops to 24.7 kHz for 2,450 watts, because it gets more power by moving closer to the circuit's natural resonant frequency. The note adds that switching frequencies in these converters can approach 100 kHz.

The coil's job is to make the field. The heat comes later, somewhere else.

## The field reaches into the pan

A changing magnetic field pushes on the electrons in any metal it passes through. The OpenStax physics textbook University Physics uses induction cooktops as its example. "The magnetic field is varied rapidly, producing eddy currents in the base of the pot, causing the pot and its contents to increase in temperature."

Eddy currents are loops of current that swirl inside a solid piece of metal, like eddies in a stream. Because the field keeps flipping, the eddy currents flip with it, tens of thousands of times a second.

## The pan's own resistance makes the heat

Metal doesn't let current flow for free. The onsemi note says the heat follows the Joule effect, the resistance times the square of the current, the same rule that heats the wire in a toaster. Here the "wire" is the bottom layer of your pan. The note describes the current as large but produced by a low voltage.

Two details make magnetic pans especially good at this. First, an alternating current crowds toward the surface of the metal, an effect called skin effect, and the note explains that this raises the metal's effective resistance. Second, a magnetic material wastes some energy every time its magnetism is flipped back and forth. The note counts these hysteresis losses as part of the heat, along with the eddy currents. It compares the whole setup to a transformer whose core is "very lossy", and here the losses are the point.

## Why some pans don't work

Bosch's induction guide is blunt. Pots and pans need to be made of ferrous metals. "Copper and aluminum won't heat up unless extra layers are added onto the base." Indesit's service FAQ says the same, asking for "a ferromagnetic material, i.e. iron or steel."

Bosch suggests a fridge magnet as the test. If it sticks to the bottom, the pan works, and even a magnet that "comes off quite easily" means the pan will still heat. For pans that fail, the onsemi note mentions an interface disk, a magnetic plate that sits between the stove and a non-induction pan.

Try it. Pick a pan, switch the zone on, then lift the pan off.

With cast iron, the water heats and the glass warms only after the pan does. Switch to aluminium and almost nothing happens. Lift the pan and the field disappears, but the glass stays warm for a while.

## Lift the pan and the power stops

Before an induction stove sends real power, it checks what's on the zone. The onsemi note describes a pan detection step in the control software, run before the power stage starts. A Teka hob manual spells out what the cook sees. "The power supply will be cut off when the pan is removed," and with no suitable pan, "there will be no transmission of power."

Models differ in the details. Electrolux's support page says that with the wrong cookware, an F symbol comes on and the zone switches itself off after 2 minutes.

## The glass stays cooler, not cold

ENERGY STAR says that because the cookware is the heat source, "the cooking top surface remains cool to the touch." That's true of the coil's part in it. The coil doesn't heat the glass.

But a pan of boiling water is still sitting on that glass. Indesit's FAQ warns that after cooking, the surface can get hot "as heat is transferred from the cooking vessel back onto the hob glass." Its induction hobs show a residual heat warning until the glass drops below 60 degrees Celsius. So the safe habit is the same as on any stove. Let the glass cool before you touch it.

## More of the heat ends up in the food

A gas flame or an electric ring makes heat first and then passes it to the pan, and some of it goes into the kitchen air on the way. Induction makes the heat in the pan's own metal. ENERGY STAR puts induction at about 85 percent efficient, against about 75 to 80 percent for electric resistance cooktops and about 32 percent for gas. That makes induction "about 3 times more efficient than gas." The onsemi note quotes slightly different US Department of Energy figures, 84 percent for induction and 74 percent for a smooth-top electric unit. The exact numbers depend on the test, but the order doesn't change.

It's a neat inversion. The stove you'd expect to be hottest stays the coolest, because the burner has moved into the pan.

## From a hot pan to the physics underneath

Induction cooking is a doorway into electromagnetism. A changing magnetic field driving current is also how a transformer works, which is why the onsemi note keeps comparing the stove to one. The kitchen side has its own rabbit holes, from how a microwave oven heats food to [why bread rises](/wait-how/why-bread-rises/). Wi-Fi shares a band with microwave ovens, as [How Wi-Fi carries data](/wait-how/how-wi-fi-works/) explains. Learnfold turns a question like these into a planned course, and each follow-up becomes a linked page. Building a course from your own question is part of Learnfold's paid subscription. It's an AI tutor and can be wrong, so [check its explanations](/guides/check-ai-explanations-for-mistakes/) against sources like the ones below.

## Quick answers

**Why doesn't an induction cooktop get hot?**

The coil under the glass doesn't heat anything directly. Its magnetic field makes currents flow in the pan's base, and the pan heats itself. The glass does warm up, but only because a hot pan sits on it. Indesit's hobs keep a residual heat warning on until the glass is below 60 degrees Celsius.

**Why don't aluminium or copper pans work on induction?**

Induction needs cookware made of a ferromagnetic metal, iron or magnetic steel. Bosch says copper and aluminium won't heat up unless extra layers are added to the base. If a fridge magnet sticks to the bottom of the pan, it should work.

**How fast does the current in an induction coil change direction?**

Tens of thousands of times a second. In an onsemi application note, one design runs between about 24.7 and 45 kHz, depending on the power setting, and switching frequencies in these converters can approach 100 kHz.

**Is induction more efficient than gas?**

Yes, by a wide margin. ENERGY STAR puts induction at about 85 percent efficient, electric resistance cooktops at about 75 to 80 percent, and gas at about 32 percent, because much of a gas flame's heat goes into the air around the pan.

## Sources

1. [AND9166/D, Induction Cooking: Everything You Need to Know (application note)](https://www.onsemi.com/pub/Collateral/AND9166-D.PDF), onsemi
2. [University Physics Volume 2, section 13.5 Eddy Currents, by Samuel J. Ling, William Moebs and Jeff Sanny](https://openstax.org/books/university-physics-volume-2/pages/13-5-eddy-currents), OpenStax
3. [2021-2022 Residential Induction Cooking Tops](https://www.energystar.gov/partner_resources/products_partner_resources/brand-owner/eta-consumers/res-induction-cooking-tops), ENERGY STAR
4. [Induction hob quick-start guide](https://www.bosch-home.com/sg/en/c/spotlight/bltf059cdb863bc8a74/highlights/hobs-hoods-journey/getting-started/induction-hobs), Bosch Home
5. [Hob FAQ](https://indesitservice.co.uk/?p=1934), Indesit Service
6. [Teka GKST80I4 instructions, page 17, Pan recognition](https://www.manualslib.mx/manual/304003/Teka-Gkst80I4.html?page=17), Teka, via ManualsLib
7. [Induction cooktop switched itself off](https://supporthub.electrolux.com.au/support-articles/article/induction-cooktop-switched-itself-off), Electrolux Australia