Magnetic Fields

1
Magnetic Fields

• Magnetism a force that exists between moving
  charges.
• Magnetism is created naturally by the spinning of
  electrons in atoms.
• Where there is electricity there is always
  magnetism!
• Magnetic field the space around a magnet in
  which magnetic forces can be detected. Unit is
  the tesla.
• Magnetic flux lines imaginary lines indicating
  the magnitude and direction of a magnetic field.
  The Weber is the unit for measuring the number of
  lines of flux.
• Magnetic domain region in which the magnetic
  fields of atoms are grouped together and aligned.
  

2
Properties

• The magnetic field lines come out of the magnet
  at its north-pole and enter the magnet at its
  south-pole.
• The direction of the magnetic field lines is the
  direction to which the north-pole of a compass
  points when it is placed in the magnetic field.
• Opposite poles attract, like poles repel each
  other.
• Magnetic field lines always form closed loops.
• The magnetic field lines continue through the
  inside of the magnet.

3
Earth as a Magnet

• The Earth acts as
• a giant magnet.
• The magnetic south pole can be found near the
  geographic north pole and vice versa.
• The magnetic poles move over time.
• The Earths poles actually reverse about every
  250,000 years on average. They last reversed
  about 780,000 years ago.

4
Movement of the South magnetic pole in the
Northern hemisphere.
5
Applications

• Navigation animals, compasses
• MRIs
• Particle Accelerators
• Maglev trains
• Aurora Borealis
• Electrical transformers
• Sticking notes to your refrigerator
• Creating electrical currents
• Audio cassettes, VHS
• Credit/Debit cards
• Health benefits?

6
Electromagnetism

• Solenoid a coil of wire wrapped around a
  conducting rod. When a current is sent through
  the wire, a magnetic field is created inside the
  rod.
• The magnetic field strength can be increased by
  increasing the current, increasing the number of
  loops, or increasing the permeability (the degree
  of magnetization of a material in response to a
  magnetic field).

7
Transformers

• As electricity flows through the wire, resistance
  decreases the voltage. There are also times that
  we want to decrease the voltage to bring it down
  to useable levels.
• Transformers allow us to do this.
• They are made out of two solenoids with varying
  amounts of loops.
• Step up transformers have fewer coils of wire in
  their primary coil than in their secondary coil
  and voltage is increased.
• Step down transformers have more coils of wire in
  their primary coil than in their secondary coil
  and voltage is decreased.