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How an induction hob heats the pan and not the surface
A changing magnetic field induces currents inside the metal of the pan, which is why the glass stays cool and why some pans do nothing.
Both approaches to induction cooking work. What differs is what they cost you, and the cost is what this sets out.
The difference in one place
- A coil under the glass induces circulating currents inside the pan base.
- Only ferromagnetic pans couple efficiently to the field.
- Heat is generated in the pan itself, so response is nearly immediate.
Currents induced in the metal
A coil beneath the glass carries alternating current at a frequency of tens of kilohertz, producing a rapidly changing magnetic field. That field induces circulating currents, called eddy currents, in any conductive material placed in it.
The electrical resistance of the pan turns those currents into heat directly within the metal. Magnetic materials add a second heating mechanism from the repeated reversal of their internal magnetic domains.
Why the pan has to be magnetic
Materials with high magnetic permeability concentrate the field into a thin surface layer, which produces strong currents in a small volume and therefore effective heating. Aluminium and copper conduct well but do not concentrate the field, so the currents spread out and generate little heat at these frequencies. A magnet sticking firmly to the base is a reliable test, which is why that advice is so widely repeated.
Pans marketed as induction compatible often have a magnetic disc bonded into an otherwise aluminium base for exactly this reason.
The glass is heated only by the pan
The ceramic surface is not magnetic and not conductive, so the field passes through it without depositing energy. Any warmth on the hob after cooking is conducted back from the pan rather than generated in the glass. That is why spills do not bake on as readily as on a radiant hob and why the surface cools quickly.
It is also why residual heat indicators are still necessary, since the surface can be genuinely hot from contact.
Control is fast because the heat is in the pan
A gas flame or a radiant element must heat itself before heating the pan, and must cool before the pan stops receiving heat. Induction changes the power delivered into the pan almost instantly, so simmer control and boil times both improve. At very low settings some hobs pulse the power on and off rather than reducing it continuously, which produces audible clicking.
Higher-quality units modulate more finely and cycle less obviously.
Noise and interference
Buzzing at high power is usually the layers of a multi-ply pan base vibrating against each other in the changing field. A lighter or warped pan buzzes more, and the sound is a property of the cookware rather than a fault in the hob.
The cooling fan for the electronics beneath the glass is the other common noise source. The field is confined closely to the coil, and regulators set exposure limits that domestic appliances are tested against.
Figures here are typical rather than guaranteed — check the spec sheet for your part.
Practical considerations
Induction hobs require a substantial dedicated electrical supply, and installation requirements vary by country and by wiring standard. Pan size should roughly match the coil, since a small pan on a large coil couples poorly and wastes energy.
At the protocol level, efficiency is high because the heat is made where it is needed, though the overall benefit depends on how your electricity is generated. Some hobs limit total output across all zones, so using several at once reduces the power available to each.
Side by side
| Consideration | What it means in practice |
|---|---|
| Currents induced in the metal | A coil under the glass induces circulating currents inside the pan base. |
| Why the pan has to be magnetic | Only ferromagnetic pans couple efficiently to the field. |
| The glass is heated only by the pan | Heat is generated in the pan itself, so response is nearly immediate. |
The takeaway
The pan is the heating element. If a magnet will not stick to it, nothing will happen.
Once you know what it is trading away, the design stops looking arbitrary.
Questions readers ask
Why does my pan buzz on an induction hob?
The layers of the pan base are vibrating in the alternating field. It is more pronounced in lighter or multi-layer pans and is not a fault.
Can I use my old pans?
Only if a magnet sticks firmly to the base. Aluminium, copper and most non-magnetic stainless pans will not heat, though interface discs exist and waste much of the advantage.
