6B_Ch_23_GG - Chapter 23 Faradays Law and Induction Michael...

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Chapter 23 Faraday’s Law and Induction
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Michael Faraday 1791 – 1867 Great experimental physicist Contributions to early electricity include – Invention of motor, generator, and transformer – Electromagnetic induction – Laws of electrolysis
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Induction An induced current is produced by a changing magnetic field There is an induced emf associated with the induced current A current is produced without a battery present in the circuit Faraday’s Law of Induction describes the induced emf
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EMF Produced by a Changing Magnetic Field A loop of wire is connected to a sensitive ammeter When a magnet is moved toward the loop, the ammeter deflects The deflection indicates a current induced in the wire The magnet is moved away from the loop The ammeter deflects in the opposite direction
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Faraday’s Experiment – Set Up A primary coil is connected to a switch and a battery The wire is wrapped around an iron ring A secondary coil is also wrapped around the iron ring There is no battery present in the secondary coil The secondary coil is not electrically connected to the primary coil
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Faraday’s Experiment – Findings At the instant the switch is closed, the galvanometer (ammeter) needle deflects in one direction and then returns to zero When the switch is opened, the galvanometer needle deflects in the opposite direction and then returns to zero The galvanometer reads zero when there is a steady current or when there is no current in the primary circuit
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Faraday’s Experiment – Conclusions An electric current can be produced by a time-varying magnetic field – This would be the current in the secondary circuit of this experimental set-up The induced current exists only while the magnetic field is changing This is generally expressed as: an induced emf is produced in the secondary circuit by the changing magnetic field – The actual existence of the magnetic field is not sufficient to produce the induced emf, the field must be changing
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Magnetic Flux and Faraday’s Law To express Faraday’s finding mathematically, the magnetic flux is used Faraday’s Law of Induction states that the emf induced in a circuit is equal to the time rate of change of the magnetic flux through the circuit
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Faraday’s Law – Statements, cont If the circuit consists of N identical and concentric loops, and if the field lines pass through all loops, the induced emf becomes – The loops are in series, so the emfs in the individual loops add to give the total emf
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Faraday’s Law – Example Assume a loop enclosing an area A lies in a uniform magnetic field The magnetic flux through the loop is Φ B = B A cos θ The induced emf is
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This note was uploaded on 02/03/2010 for the course NEUROSCI 101A taught by Professor Scheibell during the Winter '10 term at UCLA.

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6B_Ch_23_GG - Chapter 23 Faradays Law and Induction Michael...

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