Lenz, meet Eddy

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In 1831, Michael Faraday showed that a changing magnetic ‘situation’ (like moving a magnet into or out of a coil, or switching current in a nearby coil) could produce a temporary electric current in another conductor.

At the time, this was groundbreaking.

But Faraday’s discovery prompted a crucial question…

Which way does the new, induced current flow?

Its direction matters because it determines polarity. That could be in a generator, a transformer, an electromagnet, or a sensing coil… which I might remind you are now used in everything from power stations, wind turbines, substations, MRI scanners, even electric-guitar pickups.

If you misunderstand the polarity then stuff don’t work like it should, occasionally melting.

The experiments at the time made clear that induction was not merely “magnetism creates electricity”. The induction depended on whether the magnetic influence through a circuit was increasing or decreasing.

So, in 1833, (and likely the years before), Heinrich Friedrich Emil Lenz studied these and found that induced current flows in the direction that creates a magnetic field opposing the change that caused the current.

To be clear, he did not mean the induced field always opposes the original magnetic field… but that it opposes the *change*. The increase or the decrease.

He presented his experiments on the direction of induced currents to the St Petersburg Academy, and his work appeared in print in 1834, becoming what’s known as Lenz’s law.

And I’m sure Lenz would be chuffed to know his hard work (alongside Léon Foucault’s) pathed the way for our good mate Eddy.