Lenz’s, << LEHN zuhz or LEHNT suhz, >> law is a principle that relates magnetism to electric current, describing the direction of a current produced by a changing magnetic field. A magnetic field is the influence that a magnet or electric current creates in the region around it. A changing magnetic field creates a current in a conductor, such as a coil of wire, by a process called electromagnetic induction.
When a changing magnetic field creates a current, the current, in turn, creates its own magnetic field. Lenz’s law states that the current flows in such a direction that its magnetic field opposes the change in the original magnetic field. Thus, whatever device is changing the original magnetic field must do work to keep the current flowing. Lenz’s law is named for the Russian physicist Heinrich F. E. Lenz, who discovered it in 1833.
Lenz’s law explains why energy must be supplied to turn the generators that provide our electric power. An electric generator consists of wire coils that spin in a magnetic field. As the coils spin, the field changes relative to the coils, and so a current flows in them. But the field created by the current opposes the changing magnetic field and therefore opposes the spinning of the coils. Thus, unless energy is supplied to the generator, it will quickly come to a stop.
See also Electric generator ; Inductance ; Magnetism (Magnetic fields) .
