PHY213_Chapter20_Sec1to4

# PHY213_Chapter20_Sec1to4 - Chapter 20 Induced Voltages and...

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Chapter 20 Induced Voltages and Inductance

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General Physics Electromagnetic Induction Sections 1–4
General Physics Michael Faraday 1791 – 1867 Great experimental scientist Discovered electromagnetic induction Invented electric motor, generator and transformer Discovered laws of electrolysis

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General Physics Faraday’s Experiment A current can be induced by a changing magnetic field First shown in an experiment by Michael Faraday A primary coil is connected to a battery and a secondary coil is connected to an ammeter When the switch is closed, the ammeter reads a current and then returns to zero When the switch is opened, the ammeter reads a current in the opposite direction and then returns to zero When there is a steady current in the primary circuit, the ammeter reads zero WHY?
General Physics Faraday’s Startling Conclusion An electrical current in the primary coil creates a magnetic field which travels from the primary coil through the iron core to the windings of the secondary coil When the primary current varies (by closing/opening the switch), the magnetic field through the secondary coil also varies An electrical current is induced in the secondary coil by this changing magnetic field The secondary circuit acts as if a source of emf were connected to it for a short time It is customary to say that an induced emf is produced in the secondary circuit by the changing magnetic field

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General Physics Magnetic Flux The emf is actually induced by a change in the quantity called the magnetic flux rather than simply by a change in the magnetic field Magnetic flux is defined in a manner similar to that of electrical flux Magnetic flux is proportional to both the strength of the magnetic field passing through the plane of a loop of wire and the area of the loop
Physics Magnetic Flux, cont Consider a loop of wire with area A in a uniform magnetic field The magnetic flux through the loop is defined as where θ is the angle between B and the normal to the plane SI units of flux are T . m² = Wb (Weber)

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## This note was uploaded on 08/25/2009 for the course PHY 213 taught by Professor Cao during the Summer '08 term at Kentucky.

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PHY213_Chapter20_Sec1to4 - Chapter 20 Induced Voltages and...

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