Electro magnetic Induction ch 21

1
Electro magnetic Induction (ch 21)

• Well cover ch 21.1 21.4
• EM Induction is where we get all this electricity
  stuff. (w/out induction there would be no ipods,
  cell phones, video games)

2
EM Induction

• Michael Faraday found that a changing magnetic
  field creates an induced current in a coil of
  wire.
• A changing magnetic field induces an emf (emf a
  voltage and hence a current)
• This induced emf is created when the magnetic
  field is moving relative to the conductor.

3
EM Induction

• Magnetic Flux is the amount of magnetic field
  crossing a given area
• F BAcosT magnetic flux
• A area, B magnetic field, and the angle is
  measured from the line (axis) perpendicular to A
  with the B field. (Flux is a maximum when it
  crosses the area perpendicular)

4
EM Induction

• Faradays Law for induction the amount of emf
  produced depends on the change in flux per time.
• EMF (or voltage) -?f/?t -?BAcosT/?t
• To create an EMF(voltage) you can change either
  the magnetic field B, the area A, or the angle
  (like rotating a magnetic inside a conductor).

5
EM Induction

• Direction of the induced emf
• The current induced is directed to create its own
  magnetic field which will oppose the changing
  flux which is inducing it (huh?)
• In other words, the current induced will always
  make a magnetic field which tries to keep things
  the way they were. (oh, thats much clearer)

6
EM Induction

• If the conductor is a coil of wire with N loops,
  then the emf-N?f/?t.

7
EM Induction

• For a moving conductor crossing a magnetic field,
  there is one more relationship on the 50,000
  green sheet
• It can be shown (look on page 590) that emf Blv
  where B magnetic field, l length of wire
  crossing the field, v velocity of that length
  of wire crossing the field.