Eddy currents. Roller coasters. High-speed trains. And how laws give us a brake (and an induction stove).
1-Minute NomNom
Induction cooking is possible because of electromagnetic induction. An alternating current runs in the coil below the cooktop. This creates a magnetic field that induces a current in the base of the pot. A substantial amount of heat is generated as a result. This heat cooks our food. (Interestingly, this same magnetic field can also be used to build brakes for roller coasters and high-speed trains, but more about that later.)
The whole process is summarized in the graphic above. You can read more about the science — simply explained — in these two 1-Minute Marvels: “Saying goodbye to the old flame” and “It’s iron, man!”.
Science in-depth
One of the reasons heat is produced in the pot base is the electrical resistance of the pot base to the induced current (like any current flowing through a material).
Another reason is that the current induced in the pot base by the magnetic field swirls around in circles like a whirlpool (see the red circles in the diagram above). As each magnetic field line induces its own current, the many swirling currents induced cause the molecules in the pot base to vibrate and generate heat.
Each swirling current is called an eddy current. The physical law describing how eddy currents are produced is called Faraday’s law of induction.
Exploded view of one eddy current and the magnetic field created
At the same time, each eddy current also creates a mini magnetic field of its own (see black circles above). According to Lenz’s law, the magnetic field created will oppose the original magnetic field that created it.
This is really electromagnetism’s version of:
1) Newton’s Third Law (for every action, there is an equal and opposite reaction)
2) Conservation of energy (energy cannot be created or destroyed; it can only change from one form to another)
The eddy current phenomenon is so useful that it is not only used in induction cooking. Scientists, engineers and designers have also used this phenomenon to create eddy current brakes.
The opposing magnetic field creates a drag force on the conductor in which it is created. If the conductor is in motion, this drag force slows down its motion. It acts like friction on it, except there is no physical contact. To give you a sense of how substantial this force is, eddy current brakes are used in high-speed trains and roller coasters to slow them down.
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photos: in order – personal; depositphotos/lorakss; ZernLiew; personal; yuran78
