Physics » Electromagnetic Induction and AC Circuits » Faraday’s Law of Induction: Lenz’s Law

Summarizing Faraday’s Law of Induction


  • Faraday’s law of induction states that the emfinduced by a change in magnetic flux is

    \(\text{emf}=-N\cfrac{\Delta \Phi }{\Delta t}\)

    when flux changes by \(\Delta \Phi \) in a time \(\Delta t\).

  • If emf is induced in a coil, \(N\) is its number of turns.
  • The minus sign means that the emf creates a current \(I\) and magnetic field \(B\) that oppose the change in flux \(\Delta \Phi \) —this opposition is known as Lenz’s law.


Faraday’s law of induction

the means of calculating the emf in a coil due to changing magnetic flux, given by \(\text{emf}=-N\cfrac{\mathrm{\Delta \Phi }}{\mathrm{\Delta t}}\)

Lenz’s law

the minus sign in Faraday’s law, signifying that the emf induced in a coil opposes the change in magnetic flux

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