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Michael Faraday (1791-1867)

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Lenz s Law The current induced in a conductor by an external magnetic field will always have a magnetic field from the induced current to reduce the change in flux. – PowerPoint PPT presentation

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Title: Michael Faraday (1791-1867)


1
Michael Faraday (1791-1867)
  • An English Physicist and Chemist who discovered
    that electricity can be generated by moving a
    conductor through a magnetic field or by moving a
    magnetic field pass a conductor.

2
Magnetic Flux
  • A measure of the amount of magnetic field lines
    passing a certain area.
  • The SI system unit for magnetic flux is a Weber
    (Wb) or Tm2 (Telsa times meters squared)
  • Denoted by the capital Greek letter phi, F.
  • Magnetic Flux is a scalar quantity.
  • FBA cos?, ? is the angle between the magnetic
    field and a normal to the plane of the area.

A magnetic field of 3.5 T passes through an area
of 2.0 m2. How much flux passes through the
area given that the field lines passes
perpendicular to the plane of the area. F
BAcos ? 3.5 T(2.0 m2)cos 0 7.0 Webers 7.0
Wb
Magnetic flux (field lines) passing thru an area
normal
3
Faradays Law of Electromagnetic Induction
  • A changing magnetic flux induces an EMF
    (electromotive force/voltage/potential
    difference) in the area surrounding the flux.

N number of turns (loops) of wire
4
Methods to Induce an EMF
Continually changing the magnetic field strength
1.
Change the area exposed to a constant
magnetic field.
2.
Move a conductor with a length, l, exposed to
a magnetic field at a velocity, v.
3.
5
Changing the Strength of the Magnetic Field
S N
S N
Motion away from area
Motion towards area
Magnet moves closer to area
Magnet moves farther from area
Increasing the flux passing through the
conducting area
Decreasing the flux passing through the
conducting area
  • A voltage/EMF results in the conducting area and
    as a result as a current.
  • The magnetic field change can be achieved by
    moving a magnetic (steady magnetic field) closer
    and farther away from the conducting area.

6
Changing the Area Exposed to the Magnetic Field
S N
Induced EMF/voltage increased
Increasing Flux change
S N
S N
Zero flux passing through area
Maximum EMF/voltage induced
7
Another Method of Changing the Area Exposed to
the Magnetic Field
All sides of the wire are exposed
Moving the wire will change the flux through the
area thus inducing an EMF/voltage in the wire.
Moveable exposed wire
voltage
8
Another Method of Changing the Magnetic Field
Strength and Area Exposed to the Magnetic Field
9
Moving a Conductor Through a Uniform Magnetic
Field
?w through field
l
B
v
e EMF voltage Blv sin ?
B magnetic field strength l length of wire
exposed to the magnetic field v the speed of
the area through the magnetic field T angle
between velocity direction and magnetic field
10
How an Electrical Generator Works?
Generator a device that converts mechanical
energy to electrical energy.
Generator Animation
Power generation animation
11
Lenzs Law
  • The current induced in a conductor by an external
    magnetic field will always have a magnetic field
    from the induced current to reduce the change in
    flux.

S N
motion
Which way will the current travel? (clockwise
or counterclockwise)
Conducting area
12
Lenzs Law
  • The current induced in a conductor by an external
    magnetic field will always have a magnetic field
    that opposes the change in magnetic flux causing
    the induction.

I
T he magnetic field from the magnetic
x
x
I
S N
x
x
x the opposing magnetic field caused from the
induced current.
x
I
x
x
x
x
x
motion
I
Use the right hand rule on the induced magnetic
field to determine the current direction.
The magnetic field in the wire opposing the
original magnetic field causing the induction
13
Lenzs Law
  • Consider if the opposite occurred.

I
T he magnetic field from the magnetic
x
x
I
What would happen?
S N
x
x
x the opposing magnetic field cause from the
induced current.
x
I
x
x
x
x
x
motion
I
Use the right hand rule on the induced magnetic
field to determine the current direction.
Hypothetical magnetic field induced in the wire
14
Lenzs Law Example
motion
View direction
N
N
S
clockwise
What is the pole induced on the right side of the
metal bar in the solenoid? What is the direction
of the current as viewed towards the right?
15
Modification of Faradays Law Due to Lenzs Law
The negative sign takes into account that the
voltage opposes the change In flux
16
Electromagnetic Wave
  • A changing electric field will induce a changing
    magnetic field.
  • A changing magnetic field will induce a changing
    electric field.

Electromagnetic field animation
Electromagnetic Animation 1
Electromagnetic field Animation 2
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