## Wednesday, November 14, 2012

### L is for Lenz

Engineers use the character "L" as the variable symbolizing inductance. This is in honor of the physicist Heinrich Lenz.If you didn't already guess... he made a few contributions in early research regarding inductance.

Heinrich Friedrich Emil Lenz was born in 1804, in a town then known as Dorpat, which we now call Tartu, Estonia, but was then decidedly part of the Russian Empire. (as were again after WII) I only not the geography lesson because he studied  chemistry and physics at the University of Dorpat. After graduating he was part of a crew of scientists aboard the ship Predpriyatiye under Captain Otto von Kotzebue. The journey circumnavigated Africa and did a lap of the Pacif c before returning home The journey took from 1823 to 1826. The Predpriyatiye was a warship taking reinforcements to Kamchatka. But Lenz still got to be a part of a team studying geography, ethnography and natural history. His part was studying climate conditions and the properties of seawater which he summarized in a not-so-riveting memoir.

Things got more exciting when Lenz began studying electromagnetism in 1831. He was teaching at a secondary school in St. Petersburg called Petrischule. 1834, he discovered a directional relationship between induced magnetic fields and current. We now call this Lenz's Law. Michael Faraday had already discovered that induction existed but he stopped there. Lenz quantified the relationship in an equation that determines the direction of induced currents.In sum: the direction of a current that is induced by an electromagnetic force always opposes the direction of the electromagnetic force that produces it.

Imagine the classic physics demonstration If magnet moves toward a conductive but nonmagnetic material, say a copper bar, two things happen. First , the moving magnetic field penetrates the copper bar and induces eddy currents in the conductor. Then those eddy currents in the conductor generates their own magnetic field, which opposes the magnetic field of the magnet.

This principle is how many devices function: stoplight sensors, metal detectors, and even why radio reception changes as you approach the antenna. His pioneering work in electromagnetic induction is now considered fundamental to electronics. He went on to independently discover Joule's law in 1842, just a year after James Prescott Joule discovered ti himself.  Lenz went on to teach at the University of St. Petersburg, Russia, where he later became as the Dean of Mathematics and Physics from 1840 to 1863 and where he later served as Rector until his death in 1865.