(1804-1865) Russian Theoretical and Experimental Physicist (Classical Electromagnetism, Geophysics)
Heinrich Lenz was a Russian physicist who contributed a significant chapter to the evolving story of electromagnetism that physicists throughout Europe were piecing together in the 1800s. The fundamental law that he discovered, which later became known as Lenz’s law, revealed that the phenomenon of electromagnetic induction, as described earlier by michael faraday, obeyed the law of conservation of energy.
Lenz was born in Dorpat, now Tartu, Estonia, on February 12, 1804. After completing his secondary education at the age of 16, he entered the University of Dorpat, where he studied chemistry and physics. In 1923, while still a student, he managed to obtain the post of geophysical scientist on Otto von Kotzebue’s third expedition around the world. For the next three years he took advantage of this unique opportunity to investigate geophysical phenomena. He studied climatic conditions such as barometric pressure, finding the areas of maximal and minimal pressure that exist in the Tropics and determining the overall climatic pattern. He also made extremely accurate measurements of the salinity, temperature, and specific gravity of seawater. He discovered areas of maximal salinity on both sides of the equator in the Atlantic and Pacific Oceans and established the differences in salinity between these oceans and the Indian Ocean. On a later expedition, to the Caucasus in southern Russia in 1829, he studied the area’s natural resources, measured mountain heights, and measured the level of the Caspian Sea. No one would obtain observations of the ocean more accurate than Lenz’s until the next century.
When he returned to Saint Petersburg, with his expedition findings to his credit, Lenz was admitted to the prestigious Saint Petersburg Academy of Science, on an apprentice level; by 1834, he would rise to the status of full academician. He began to study electromagnetism in 1831, after Faraday and joseph henry independently discovered electromagnetic induction. His first major discovery, published in 1833, was the famous Lenz’s law, which states that the direction of a current that is induced by an electromagnetic force always opposes the direction of the electromagnetic force that produces it. This occurs because a current induced by a moving magnet or coil flows in such a direction that it, in turn, induces a magnetic field that opposes the motion of the magnet or coil inducing the current.
Lenz described the dynamics of this process as follows: thrusting a pole of a permanent bar magnet through a coil of wire induces an electric current in the coil; the current in turn sets up a magnetic field around the coil, making it a magnet. Lenz’s law indicates the direction of the induced current. Because like magnetic poles repel each other, when the north pole of the bar magnet approaches the coil, the induced current flows in such a way as to make the side of the coil nearer the pole of the bar magnet itself a north pole to oppose the approaching bar magnet. When the bar magnet is withdrawn from the coil, the induced current reverses itself, and the near side of the coil becomes a south pole to produce an attracting force on the receding bar magnet. A small amount of work, therefore, is done in pushing the magnet into the coil and in pulling it out against the magnetic effect of the induced current. The small amount of energy represented by this work manifests itself as a slight heating effect, the result of the induced current’s encountering resistance in the material of the coil. Lenz’s law thus upholds the general principle of the conservation of energy. If the current were induced in the opposite direction, its action would spontaneously draw the bar magnet into the coil in addition to producing the heating effect, thereby violating conservation of energy.
In 1833, Lenz investigated the way electrical resistance of metals changes with temperature and showed that an increase in temperature increased resistance. Around the same time, he studied the heat generated by current flowing in metals and discovered, independently of james prescott joule, the law now known as Joule’s law, which describes the proportional relationship between the production of heat and the square of the current. In the context of these experiments, he worked on establishing the unit for the measurement of resistance.
During the same period, he also worked on the application of certain theoretical physics principles to engineering design and on formulation of programs for geographical expeditions. In 1836, he became a professor at Saint Petersburg University and from 1840 to 1843 was dean of mathematics and physics. . Lenz died of a stroke just before his 61st birthday, while on vacation in Rome, on February 10, 1865.
Lenz’s law helped hermann ludwig ferdinand von helmholz formulate the law of conservation of energy. It is applied today in electrical machines such as generators and electric motors.
