Lenz, Heinrich Friedrich Emil (1804–1865)

Russian physicist who in 1833 formulated Lenz's law, a fundamental law of electromagnetism. He also found that the strength of a magnetic field is proportional to the strength of the magnetic induction.

Lenz was born and educated in Dorpat (now Tartu, Estonia). As geophysical scientist, he accompanied Otto von Kotzebue (1787–1846) on his third expedition around the world 1823–26. On his return, Lenz joined the St Petersburg Academy of Science, and from 1840 held posts at the University of St Petersburg.

On his voyage with Kotzebue, Lenz studied climatic conditions such as barometric pressure, and made extremely accurate measurements of the salinity, temperature, and specific gravity of sea water. On a later expedition he measured the level of the Caspian Sea.

Lenz's studies of electromagnetism date from 1831. Lenz's law is in fact a special case of the law of conservation of energy. If the induced current were to flow in the opposite direction, it would assist the motion of the magnet or wire and energy would increase without any work being done, which is impossible.

Lenz also studied the relationship between heat and current and discovered, independently of English physicist James Joule, the law now known as Joule's law.