Magnetic Effects

1
Magnetic Effects

• Forces between electric charges in motion.

2
Familiar Ideas.

• An phenomenon apparently unrelated to electricity
  is magnetism.
• The interaction of compasses with the earth's
  magnetic field.
• Fridge magnets or magnets on children's toys.

3
Magnetic forces.

• There are two types of magnetic poles,
  conventionally called North and South.
• Like poles repel, and opposite poles attract.

4
Magnetism differs from electricity.

• Unlike electric charges, magnetic poles always
  occur in North-South pairs.
• There are no magnetic monopoles.

5
Weber's Theory

• Considers the molecular alignment of the
  material.
• All magnetic substances are composed of tiny
  molecular magnets.
• Unmagnetized material has the magnetic forces of
  its molecular magnets neutralized by adjacent
  molecular magnets.
• Eliminating any magnetic effect.

6
A magnetized material.

• Most of its molecular magnets lined up.
• Molecules thus aligned will then have one
  effective north pole, and one effective south
  pole.

7
Domain Theory.

• Based on the electron spin principle.
• Atoms contain one or more orbital electrons.
• Electrons have angular momentum (spin).
• An electron has a magnetic field about it along
  with an electric field.
• The effectiveness of the magnetic field of an
  atom is determined by the number of electrons
  spinning in each direction.

8
Electron Spin

• If equal numbers of electrons spin in opposite
  directions, the atom has no magnetic qualities.
• If more electrons spin in one direction than
  another, the atom is magnetized.

9
Domain Accumulation.

• If a material is subjected to an external
  magnetic field, the domains will align.
• More and more domains join the domain as the
  internal field strengthens.

10
Magnetic Properties of Solids

• Diamagnetism.
• Paramagnetism.
• Ferromagnetism.

11
Diamagnetism.

• Diamagnetism is a property of all materials,
  which opposes applied magnetic fields, but is
  very weak.
• Orbital motion of electrons creates tiny atomic
  current loops, which produce magnetic fields.
• When an external magnetic field is applied to a
  material, these current loops will tend to align
  in such a way as to oppose the applied field.

12
Paramagnetism.

• Materials exhibit a magnetization which is
  proportional to the applied magnetic field in
  which the material is placed.
• In most materials the magnetic moments of the
  electrons cancel, but in materials which are
  classified as paramagnetic, the cancellation is
  incomplete.

13
Ferromagnetism.

• Iron, nickel, cobalt and some of the rare earth
  elements.
• Exhibit a long range ordering phenomenon at the
  atomic level.
• Causes the unpaired electron spins to line up
  parallel with each other in a region called a
  domain.
• A small externally imposed magnetic field can
  cause the magnetic domains to line up with each
  other and the material is said to be magnetized.

14
Permanent Magnetism

• Ferromagnets will tend to stay magnetized.
• This tendency to "remember their magnetic
  history" is called hysteresis.
• The temperature where the ferromagnetic property
  disappears as a result of thermal agitation. This
  temperature is called the Curie temperature.

15
Magnetic Fields

• The space surrounding a magnet where magnetic
  forces act.
• All magnetic fields have two poles (N and S).

16
Opposite Poles Attract.
17
Like Poles Repel
18
Magnetic Field

• Breaking a magnet in half does not separate the
  poles but produces two magnets with two "poles"
  each.
• The "north" and "south" poles of a magnet or a
  magnetic dipole are labeled similar to north and
  south poles of a compass needle.
• This magnetic field continues inside of magnet
  (so there are no actual "poles" anywhere inside
  or outside of a magnet).

19
The Earth's Magnetic Field.
20
Origin of the Magnetic Field

• The origin of the Earth's magnetic field is not
  completely understood.
• Electrical currents produced by the coupling of
  convective effects and rotation in the spinning
  liquid metallic outer core of iron and nickel.
• This mechanism is termed the dynamo effect.

21
The Magnetosphere
22
The Nature of the Magnetosphere

• Two factors determine the structure and behavior
  of the magnetosphere
• The internal field of the Earth (its "main
  field") appears to be generated in the Earth's
  core by a dynamo process.
• The solar wind is a fast outflow of hot plasma
  from the sun in all directions which distorts the
  symmetry of the magnetic field of the Earth in
  space.

23
Radiation Belts.

• The "inner radiation belt" of protons with
  energies in the range 10-100 MeV (million
  electron volts), called the Van Allen belt. It is
  centered on field lines crossing the equator
  about 1.5 RE from the Earth's center.
• A population of trapped ions and electrons was
  observed on field lines crossing the equator at
  2.5-8 RE. The high-energy part of that population
  (about 1 MeV) became known as the "outer
  radiation belt.

24
Magnetospheric Protection

• The magnetosphere deflects radiation and solar
  wind particles.
• Coronal Mass Ejections (CME) can compress the
  magnetosphere and expose satellites and parts of
  the earth to radiation and energetic particles
  from the sun.
• CME events are sometimes called solar storms.

25
Solar Storms (space weather)

• Space weather refers to violent transfers of
  matter and energy from the sun to the Earth.
• 4 billion in satellite losses can be traced to
  space weather damage.
• The last major space storm caused an electrical
  blackout in Quebec.
• Solar flares have cost the airline industry
  millions of dollars.

26
Satellite Losses

• Solar Panel Degradation. Energetic particles from
  the sun, produce physical damage to silicon-based
  solar cells.
• Premature Atmospheric Reentry. Solar storms heat
  the upper atmosphere causing increased drag which
  accelerates orbit decay.
• Sudden Event Upsets. High-energy particles such
  as cosmic rays or protons from solar flares, do
  considerable internal damage to spacecraft.

27
Electrical Blackouts

• Space weather disturbances cause Geomagnetically
  Induced Currents , these GICs can enter a
  transformer through its Earth ground connection.
• The added DC current to the transformer causes
  the relationship between the AC voltage and
  current to change.
• One hundred amperes of GIC current or less will
  cause a transformer to overload.
• Space weather events can damage equipment over
  wide geographic regions.

28
Losses to the Airlines

• Most airlines use polar routes for
  intercontinental flights to save time and fuel.
• During a solar flare, radiation levels at the
  poles increase significantly.
• Airlines route flights at lower altitudes at a
  much greater cost in fuel (3,000 extra gallons at
  a cost of over 10K).