# Lenz's law

Lenz's law tells the direction of a current in a conductor loop induced indirectly by the change in magnetic flux through the loop. Scenarios a, b, c, d and e are possible. Scenario f is impossible due to the law of conservation of energy. The charges (electrons) in the conductor are not pushed in motion directly by the change in flux, but by a circular electric field (not pictured) surrounding the total magnetic field of inducing and induced magnetic fields. This total magnetic field induces the electric field.

Lenz's law (pronounced s/), named after the physicist Heinrich Friedrich Emil Lenz who formulated it in 1834,[1] states that the direction of current induced in a conductor by a changing magnetic field due to induction is such that it creates a magnetic field that opposes the change that produced it.

${\displaystyle {\mathcal {E}}=-{\frac {\partial \Phi }{\partial t}},}$

which indicates that the induced electromotive force (${\displaystyle {\mathcal {E}}}$) and the change in magnetic flux (${\displaystyle \partial \Phi }$) have opposite signs.[2] It is a qualitative law that specifies the direction of induced current but says nothing about its magnitude. Lenz's law explains the direction of many effects in electromagnetism, such as the direction of voltage induced in an inductor or wire loop by a changing current, or why eddy currents exert a drag force on moving objects in a magnetic field.

Lenz's law can be seen as analogous to Newton's third law in classic mechanics.[3]

For a rigorous mathematical treatment, see electromagnetic induction and Maxwell's equations.

## Opposing currents

If a change in the magnetic field of current i1 induces another electric current, i2, the direction of i2 is opposite that of the change in i1. If these currents are in two coaxial circular conductors 1 and 2 respectively, and both are initially 0, then the currents i1 and i2 must counter-rotate. The opposing currents will repel each other as a result.

Lenz's law states that the current induced in a circuit due to a change or a motion in a magnetic field is so directed as to oppose the change in flux and to exert a mechanical force opposing the motion.

### Example

Currents bound inside the atoms of strong magnets can create counter-rotating currents in a copper or aluminum pipe. This is shown by dropping the magnet through the pipe. The descent of the magnet inside the pipe is observably slower than when dropped outside the pipe.

When a voltage is generated by a change in magnetic flux according to Faraday's Law, the polarity of the induced voltage is such that it produces a current whose magnetic field opposes the change which produces it. The induced magnetic field inside any loop of wire always acts to keep the magnetic flux in the loop constant. In the examples below, if the flux is increasing, the induced field acts in opposition to it. If it is decreasing, the induced field acts in the direction of the applied field to oppose the change.

Other Languages
العربية: قانون لينز
asturianu: Llei de Lenz
беларуская: Правіла Ленца
català: Llei de Lenz
čeština: Lenzův zákon
dansk: Lenz' lov
español: Ley de Lenz
Esperanto: Leĝo de Lenz
euskara: Lenzen legea
فارسی: قانون لنز
한국어: 렌츠의 법칙
hrvatski: Lenzovo pravilo
italiano: Legge di Lenz
עברית: חוק לנץ
македонски: Ленцов закон
Nederlands: Wet van Lenz
norsk: Lenz' lov
norsk nynorsk: Lenz-lova
Piemontèis: Lej ëd Lenz
polski: Prawo Lenza
português: Lei de Lenz
Simple English: Lenz's law
slovenčina: Lenzov zákon
slovenščina: Lenzovo pravilo
српски / srpski: Ленцов закон
srpskohrvatski / српскохрватски: Lencov zakon
svenska: Lenz lag
Türkçe: Lenz yasası
українська: Правило Ленца
Tiếng Việt: Định luật Lenz