Faradays law

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Faradays law

• Flux
• Faradays law
• Lenzs law
• Examples
• Generator

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Electromagnetic Induction

• Magnetic Flux

If B is constant
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Electromagnetic Induction
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Electromagnetic Induction
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Electromagnetic Induction

• Faradays Law
• Last time we ended class by dropping a magnet
  through a coil. Lets do it again.

coil
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Electromagnetic Induction

• Faradays Law
• This phenomena is called electromagnetic
  induction and is described by Faradays law.
  Write Faradays law.
• In order to understand Faradays law we need to
  understand the concept of magnetic flux. Write
  the definition of magnetic flux.

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Electromagnetic Induction

• Faradays Law
• The magnetic flux is exactly like the electric
  flux we studied in Gausss law. The flux is
  defined in terms of a vector area dA. Describe
  the magnitude and direction of this vector.

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Electromagnetic Induction

• Lenzs Law
• The direction of the emf and thus the current is
  given by Lenzs law. The statement in bold in
  the center of page 789 is a statement of Lenzs
  law. Use this to find the direction of the
  current. If you are looking down on the loop
  from above, is the current flowing clockwise or
  counter clockwise? Explain.

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Electromagnetic Induction

• Lenzs Law

The magnetic is moving away from the coil so the
magnetic field is decreasing, thus the current is
in a direction to off-set the decrease.
The magnetic is moving toward the coil so the
magnetic field is increasing, thus the current is
in a direction to off-set the increase.
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Electromagnetic Induction

• Faradays Law

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Electromagnetic Induction

• Faradays Law

Does it make a difference if it is the magnetic
moving or the coil? This was a major point in
Einsteins theory of relativity.
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Electromagnetic Induction

• Faradays Law
• What about these two cases?

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Electromagnetic Induction

• Faradays Law

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Electromagnetic Induction

• Faradays Law
• Show that when you integrate the emf, e with
  respect to time you get the average change in
  flux in time ?t.

Average value
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Electromagnetic Induction

• Problem
• A circular wire loop with a radius of 20 cm. is
  in a constant magnetic field of 0.5 T .
• What is the flux through
• the loop if the normal to
• the loop makes an angle
• of 300 with the magnetic
• field?

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Electromagnetic Induction

• Problem
• The magnetic field increases from 0.5 T to 2.5 T
  in 0.8 seconds. What is the average emf, e(t)
  induced in the loop.

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Student Workbook
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Student Workbook
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Student Workbook
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Student Workbook
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Student Workbook
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Student Workbook
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Class Questions
Is there an induced current in this circuit? If
so, what is its direction?
1. Yes, clockwise 2. Yes, counterclockwise 3. No
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Class Questions
Is there an induced current in this circuit? If
so, what is its direction?
1. Yes, clockwise 2. Yes, counterclockwise 3. No
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Class Questions
1. F2 F4 gt F1 F3 2. F3 gt F2 F4 gt F1 3.
F3 gt F4 gt F2 gt F1 4. F4 gt F2 gt F1 F3 5. F4 gt
F3 gt F2 gt F1
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Class Questions
1. F2 F4 gt F1 F3 2. F3 gt F2 F4 gt F1 3.
F3 gt F4 gt F2 gt F1 4. F4 gt F2 gt F1 F3 5. F4 gt
F3 gt F2 gt F1
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Class Questions
A current-carrying wire is pulled away from a
conducting loop in the direction shown. As the
wire is moving, is there a cw current around the
loop, a ccw current or no current?
1. There is a clockwise current around the
loop. 2. There is a counterclockwise current
around the loop. 3. There is no current around
the loop.
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Class Questions
A current-carrying wire is pulled away from a
conducting loop in the direction shown. As the
wire is moving, is there a cw current around the
loop, a ccw current or no current?
1. There is a clockwise current around the
loop. 2. There is a counterclockwise current
around the loop. 3. There is no current around
the loop.
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Class Questions
A conducting loop is halfway into a magnetic
field. Suppose the magnetic field begins to
increase rapidly in strength. What happens to the
loop?
1. The loop is pushed upward, toward the top of
the page. 2. The loop is pushed downward, toward
the bottom of the page. 3. The loop is pulled to
the left, into the magnetic field. 4. The loop is
pushed to the right, out of the magnetic
field. 5. The tension is the wires increases but
the loop does not move.
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Class Questions
A conducting loop is halfway into a magnetic
field. Suppose the magnetic field begins to
increase rapidly in strength. What happens to the
loop?
1. The loop is pushed upward, toward the top of
the page. 2. The loop is pushed downward, toward
the bottom of the page. 3. The loop is pulled to
the left, into the magnetic field. 4. The loop is
pushed to the right, out of the magnetic
field. 5. The tension is the wires increases but
the loop does not move.
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Electromagnetic Induction

• Example Induction stove
• The pan on the stove is heated by eddy currents
  produced by induction.

• Would this stove work with a ceramic bowl?
• Does the surface of the stove get hot?

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Electromagnetic Induction

• Application of Faradays Law
• Generator

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Electromagnetic Induction

• Application of Faradays Law
• Magnetic Recording

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Electromagnetic Induction

• The Most Important Point of Faradays Law
• A changing magnetic field produces
• or creates an electric field.

Two types of electric fields. One is created by
charge and the other is created by a changing
magnetic field.
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Student Workbook