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Electromagnetic Induction

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Electromagnetic Induction The Discoveries of Michael Faraday and Joseph Henry Showed That a Current Can Be Induced by a Changing Magnetic Field. – PowerPoint PPT presentation

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Title: Electromagnetic Induction


1
Electromagnetic Induction
  • The Discoveries of Michael Faraday and Joseph
    Henry Showed That a Current Can Be Induced by a
    Changing Magnetic Field.

2
Faradays Law
  • An emf is set up in a closed electric circuit
    located in a magnetic field whenever the total
    magnetic flux linking the circuit is changing.
  • This is called electromagnetic induction.
  • Induced emf
  • Induced current

3
A Galvanometer and a B-Field
  • Induced current is related to the motion of the
    conductor in the magnetic field
  • The direction of the induced current is directly
    related to the direction of motion of the
    conductor in the magnetic field
  • Direction is dependent on the motion of the
    B-field or the conductor
  • The motion of the conductor is perpendicular to
    the B-field

4
More Thoughts
  • If the conductor is moved parallel to B-field,
    the galvanometer will show no deflection, thus no
    induced emf or current.
  • If the conductor is looped several times, the
    deflection on the galvanometer will increase.
  • Thus, the rate of motion, the number of loops and
    the magnitude of the B-field vary directly with
    the magnitude of the induced current and emf.

5
Factors Affecting Emf
  • Emf induced in each coil of the conductor is
    proportional to rate of change of magnetic flux
  • Emf - DF/Dt
  • Emf -N(DF/Dt)
  • Note that negative sign indicates that induced
    emf is of such polarity as to oppose the change
    that induced it

6
Induced EMF
  • Induced current exists only if wire in a field is
    part of a circuit.
  • Thus, if F BA then F Bxl
  • So therefore, Emf - DBxl/Dt
  • But x/t v (velocity)
  • Therefore, Emf Blv

7
Faradays Law
  • The induced emf in a coil of N loops with a
    changing B field within in equal to the rate of
    change of magnetic flux times the number of loops.

8
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9
Lenzs Law
10
  • The net B-field thru a loop from a changing flux
    comes from two sources.

11
  • The original B field.
  • The B field caused by the original currentthe
    induced B field.

12
Induced B Field
  • This occurs because of the induced current.
  • This can be used to determine the polarity of the
    induced emf.

13
Lenzs Law
  • The induced emf resulting from a changing
    magnetic flux has a polarity that leads to an
    induced current whose direction is such that the
    induced B field opposes the original flux
    change.
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