An unlikely winner of the age-old debate?

It’s something that crosses everyone’s mind at least a few times in their life. What’s best to cook with: gas or electric cook tops? Now we could run through the pros and cons of each, like worrying about an open flame in the house or taking forever to boil water. But I have a wild card entry that I think takes the cake, the induction cook top. It wins in the heavily weighted category of scientific brilliance, which easily secures the overall win!

Induction cook top. Credit: anamoly23 via Flickr.

What makes them so great? Well they are about 25 – 50 % faster than traditional cookers and about 13% more energy efficient. This improved efficiency is mostly because the cooker does not actually heat up, only the pan! Now you might have heard about them, but what do you know about how they work?

I’m willing to guess not much, so I’ll try to step you through.

It all starts with magnets and electricity. Just stay with me for a bit and I promise it will all come together. The first thing you need to know about is eddy currents.

Eddy currents were first discovered by the 25th Prime Minister of France, François Arago (1786 – 1853), who was also a renowned scientist. He discovered that, if you take a magnet and its associated magnetic field (which causes things to be attracted to it), and you move this magnet in front of a conductive material, then the changing magnetic field will cause a current to flow in the conductor.

They’re called eddy currents, not because Eddy invented them, but because they move in circles!

Now if we look at this image below, we have a magnet that is moving with the green lines being the magnetic field. This moving magnet then causes little eddy currents to flow, which are the red circles below.

Eddy current diagram. Credit: Chetvorno via Wikimedia Commons

Whenever there is a closed loop of electricity, like in the eddies above, we know that all the electrical energy needs to go somewhere. Usually in the circuit, there is something like a light bulb that takes up all the energy. But in this case, it’s turned into heat – ideal for cooking!

Does that mean I have moving bar magnets in my kitchen?

Not quite. Under the cooktop are a bunch of coils, with electricity running through them. These produce magnetic fields, exactly like a bar magnet would, because of the relationship between electricity and magnetism. But since they are connected to AC power, the direction of the current keeps changing, which means so too does the magnetic field (the north and south poles flip).

When you place an induction pan on the cooktop, this changing magnetic field generates eddy currents in the base of the pan. All the electrical energy that is in the eddy currents is then dissipated as heat, just like how any of your electronics get hot. Except eddy currents are very inefficient, so they generate A LOT of heat. Which is what makes them so great to cook your food with!

You won’t just find eddy currents in the kitchen!

If you’ve ever taken the Inter-City Express or the Japanese Shinkansen trains, they use eddy currents to slow down! This is great since it requires no mechanical contact and lowers wear and tear. The same applies if you recently rode on a roller-coaster, the only reason you are alive today is because eddy currents slowed you down!

Japanese Shinkansen bullet train. Credit: Fikri Rasyid via Unsplash

But how do they slow you down?

Well just like how the coil of electricity formed an electromagnet in the cooktop, eddy currents also have their own magnetic field, because they are circular. Think about it as if you had two magnets, you keep one fixed to a table and you try to slide the other one past. The result is that the moving magnet is attracted to the fixed one and slowed to a halt when they stick together!

This is the same idea behind how the fast trains and rollercoasters can slow themselves down, using magnets and eddy currents! In fact, the very power tools that built the building you’re sitting in today, probably used eddy currents to slow their motor when turned off.

So, what can we take away from today? (1) Induction cookers are indeed the coolest thing you could possibly put in your kitchen (2) François Arago was one multi-talented Prime Minister of France.