Faraday's Law of Induction

This is part of the HSC Physics course under the topic Electromagnetic Induction.

HSC Physics Syllabus

  • analyse qualitatively and quantitatively, with reference to energy transfers and transformations, examples of Faraday's Law and Lenz's Law `\varepsilon = -N (∆\phi)/(∆t)`, including but not limited to:
– the generation of an electromotive force (emf) and evidence for Lenz's Law produced by the relative movement between a magnet, straight conductors, metal plates and solenoids
– the generation of an emf produced by the relative movement or changes in current in one solenoid int he vicinity of another solenoid

Faraday's Law of Induction

This video will analyse qualitatively and quantitatively examples of Faraday's Law. It introduces the equation `\varepsilon = -N (∆\phi)/(∆t)`.


Discovery of Electromagnetic Induction

Michael Faraday wrapped wires around opposite ends of a soft iron ring, with one attached to a power source and another to a voltmeter. After the switch is closed, the current through the first wire caused a temporary pulse of induced current to be created in the opposite wire, which was detected by the voltmeter.



This is because the first wire's current created a magnetic field, which caused the free moving electrons (unaffected by potential difference) in the opposite wires to experience a magnetic force.




This movement of electrons creates current. However, after a short while, the movement of electrons will stop as the constant force causes them to end up in a particular extremity of the conductor e.g. one end of a straight conductive rod. Thus, a current is only induced when the magnetic field, experienced by the conductor is changing.


This is called Faraday’s Law of Induction, which states that an emf is induced in a conductor when it experiences change in magnetic flux. In any closed electrical conductor, this emf leads to a current. The magnitude of the emf is proportional to the rate of magnetic flux change. Faster the change, greater the induced current.


$$\varepsilon = -N\frac{∆\phi}{∆t}$$


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