Michael Faraday
1791–1867 · 1831
A changing current in one coil makes a current in another
Faraday left school at thirteen and was apprenticed to a bookbinder, which is how he came to read the books he was binding. He talked his way into the Royal Institution as a laboratory assistant and stayed for most of his life.
In 1831 he wound two coils on an iron ring and found that switching the current in the first coil made a current jump in the second — not while the current flowed, but at the moment it changed. Induction is a response to change, which is why his ring worked and a steady current would not have.
He had almost no mathematics. He described what he saw in terms of lines of force, and it took Maxwell, thirty years later, to put that picture into equations.
The relay on this board is his ring with a job: a current in the coil pulls an iron armature and closes contacts in a circuit it never touches.
The thing you can build here
One coil, two circuits →A small current in the coil switches a much larger one beside it, with no electrical connection between them.
Sources
- Faraday, Experimental Researches in Electricity, Series I, Philosophical Transactions of the Royal Society, 1832.
- Faraday’s laboratory notebook, 29 August 1831.