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Faraday's Law of Induction and Lenz' Law
Faraday's law of induction states that the EMF induced by a change in magnetic flux is $EMF = N\frac{\Delta \Phi}{\Delta t}$ , when flux changes by Δ in a time Δt.
Learning Objectives

Identify devices with the operation based on the Faraday's law of induction

Express the Faraday’s law of induction in a form of equation
Key Points

The minus in the Faraday's law means that the EMF creates a current I and magnetic field B that oppose the change in flux Δthis is known as Lenz' law.

Faraday's law of induction is the fundamental operating principle of transformers, inductors, and many types of electrical motors, generators, and solenoids.

Faraday's law states that the EMF induced by a change in magnetic flux depends on the change in flux Δ, time Δt, and number of turns of coils.
Terms

electromotive force
(EMF)—The voltage generated by a battery or by the magnetic force according to Faraday's Law. It is measured in units of volts, not newtons, and thus, is not actually a force.

solenoid
A coil of wire that acts as a magnet when an electric current flows through it.

flux
The rate of transfer of energy (or another physical quantity) through a given surface, specifically electric flux or magnetic flux.
Full Text
Faraday's Law of Induction
Faraday's law of induction is a basic law of electromagnetism that predicts how a magnetic field will interact with an electric circuit to produce an electromotive force (EMF). It is the fundamental operating principle of transformers, inductors, and many types of electrical motors, generators, and solenoids.
Faraday's experiments showed that the EMF induced by a change in magnetic flux depends on only a few factors. First, EMF is directly proportional to the change in flux Δ. Second, EMF is greatest when the change in time Δt is smallest—that is, EMF is inversely proportional to Δt. Finally, if a coil has N turns, an EMF will be produced that is N times greater than for a single coil, so that EMF is directly proportional to N. The equation for the EMF induced by a change in magnetic flux is
This relationship is known as Faraday's law of induction. The units for EMF are volts, as is usual.
Lenz' Law
The minus sign in Faraday's law of induction is very important. The minus means that the EMF creates a current I and magnetic field B that oppose the change in flux Δthis is known as Lenz' law. The direction (given by the minus sign) of the EMF is so important that it is called Lenz' law after the Russian Heinrich Lenz (1804–1865), who, like Faraday and Henry, independently investigated aspects of induction. Faraday was aware of the direction, but Lenz stated it, so he is credited for its discovery .
Energy Conservation
Lenz' law is a manifestation of the conservation of energy. The induced EMF produces a current that opposes the change in flux, because a change in flux means a change in energy. Energy can enter or leave, but not instantaneously. Lenz' law is a consequence. As the change begins, the law says induction opposes and, thus, slows the change. In fact, if the induced EMF were in the same direction as the change in flux, there would be a positive feedback that would give us free energy from no apparent source—conservation of energy would be violated.
Key Term Reference
 Law
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 circuit
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 conservation
 Appears in this related concepts: Conservation of Mechanical Energy, Museums and Private Collections, and Linear Momentum
 current
 Appears in this related concepts: Reporting LongTerm Liabilities, Magnetic Force Between Two Parallel Conductors, and The Junction Rule
 energy
 Appears in this related concepts: Energy Transportation, Surface Tension, and Introduction to Work and Energy
 equation
 Appears in this related concepts: A General Approach, Equations and Inequalities, and Equations and Their Solutions
 force
 Appears in this related concepts: Work Done by a Variable Force, Driven Oscillations and Resonance, and Glancing Collisions
 induction
 Appears in this related concepts: Sociology and the Common Sense, The Law of Universal Gravitation, and Reasoning
 inductor
 Appears in this related concepts: Induced Charge, RL Circuits, and Inductance
 magnetic field
 Appears in this related concepts: Maxwell's Predictions and Hertz' Confirmation, Ampere's Law: Magnetic Field Due to a Long Straight Wire, and BrainScanning Techniques
 magnetic flux
 Appears in this related concepts: Inductance, Motional EMF, and Transformers
 positive feedback
 Appears in this related concepts: Mechanical Work and Electrical Energy, Homeostatic Control, and Convection
 transformer
 Appears in this related concepts: Sources of EMF and Ferromagnetism
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Cite This Source
Source: Boundless. “Faraday's Law of Induction and Lenz' Law.” Boundless Physics. Boundless, 14 Nov. 2014. Retrieved 30 Apr. 2015 from https://www.boundless.com/physics/textbooks/boundlessphysicstextbook/inductionaccircuitsandelectricaltechnologies22/magneticfluxinductionandfaradayslaw161/faradayslawofinductionandlenzlaw5696693/