Have you ever tried to jumpstart a car using cheap jumper leads?
What happened? You probably found that the leads became very hot, possibly even melted. The reason for this is that when electricity passes through a metal, there is always some resistance. That resistance can generate heat. This is why many electrical components need a heatsink, and all computers these days have a fan of some sort.
This, of course, is how electrical heaters work. You pass current through an element, the element gets hot, and you become toasty warm if you are sitting in front of it.
The ability to directly control heat is generally seen as the single greatest advantage of gas cookers over electrical cookers. The gas gives instant heat, and can be instantly turned down to reduce the heat. Electric elements, on the other hand, heat up slowly, and when you turn them down, they take a little while to cool.
This is where induction heating comes into its own. If we can pass electrical current through a saucepan, we can heat it in just the same way that we heat the wire in a heating element.
But how do we make current flow through a saucepan?
We do this by using the principle of electromagnetic induction, something that was discovered by the one and only Michael Faraday (the father of electricity) in the early 19th century.
Essentially, the induction cooker contains a copper coil. When current is passed through the copper coil, it generates an electric field and a magnetic field. If it finds a ferromagnetic steel in the vicinity (steel or iron) the electric field generated by the copper will induce an electrical current in the steel.
So this is how and induction heater works – a copper coil under a glass ceramic cooktop generates an electric field. The steel saucepan that is sitting on top of the cooktop has a current induced in it. This induced current generates heat, and this heat is responsible for heating the contents of the saucepan. To increase or decrease the heat rapidly, all we have to do is change the current flowing through the induction coil.
But induction heaters have other advantages. Notably, they are safer, since the only thing that is getting hot is the saucepan itself; the cooktop itself does not get hot. We have already seen that glass is a poor heat conductor – this means that it doesn’t get hot with the hot saucepan sitting on top of it.
So there you have it. But it only works on a ferromagnetic metal (something that a magnet will stick to), like steel.