Chapter 30 - Magnetic Induction - FSU Physics Department
Chapter 30 - Magnetic Induction - FSU Physics Department Chapter 30 - Magnetic Induction - FSU Physics Department
Induced emf produced by a changing flux isr r dφmξ = ∫ E ⋅dl= −cFaraday’s lawdtThe integral of E over a closed loop is the emf (orvoltage) by definition of electric potential (Chapter24).PHY2049C - Prof. Ng 2
Lenz’s lawThe negative sign in Faraday’s law tells us thedirection of the induced current (or polarity of theinduced emf). Lenz’s law states:The flux produced by the induced current whichresults from the induced emf, opposes the originalchange in flux.The underlying principle of Lenz’s law is the lawof conservation of energy.Step-by-step instructions for using Lenz's law -used to determine the direction of the(conventional) induced current in a loop.Need the following:(i) a loop(ii) (an external) magnetic field inside loop or afield that is switched on or off.1. First determine whether the magnetic flux (=BA cos θ) inside loop is decreasing, increasing orunchanged.2. a. If flux is decreasing then induced magneticfield points in the same direction as the externalfield.b. If flux is increasing then induced magneticfield points in the opposite direction as theexternal field.c. If flux is not changing, then there is no inducedcurrent.3. From the induced magnetic field use RH rule(see Fig 29-14 a) to find the direction of thecurrent.PHY2049C - Prof. Ng 3
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- Page 5 and 6: InductanceA coil that carries a cur
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Induced emf produced by a changing flux isr r dφmξ = ∫ E ⋅dl= −cFaraday’s lawdtThe integral of E over a closed loop is the emf (orvoltage) by definition of electric potential (<strong>Chapter</strong>24).PHY2049C - Prof. Ng 2
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