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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
• 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
• 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.