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).