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Magnetism

Magnetism. Single moving charge and the magnetic field it creates. Magnetic field created by a loop of wire with a current flowing through it. What causes magnetism? . The movement of any charged particle creates a magnetic field. Even the spinning of a single electron as it

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Magnetism

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  1. Magnetism

  2. Single moving charge and the magnetic field it creates

  3. Magnetic field created by a loop of wire with a current flowing through it

  4. What causes magnetism? • The movement of any charged particle creates a magnetic field. • Even the spinning of a single electron as it orbits a nucleus produces a magnetic field. • Magnetic fields of different moving charged particles then interact to produce forces of attraction or repulsion.

  5. Magnetic Domains

  6. Lodestones • Natural Magnets • Magnetite, Fe3O4 (an oxide of iron) • Ancient civilizations (Greek 590 BCE, Chinese 2600 BCE) realized that these stones would cling to iron tools. • A suspended, pivoting lodestone always pointed along the North South magnetic axis on a map.

  7. Naturally magnetic things • Magnetite crystals have been found in living organisms • · Magnetotactic bacteria! • · Migratory Bird brains!! • · Other migratory animals: bees, fish • · Human brains!!! • · YOU HAVE ROCKS IN YOUR HEAD!!!!!

  8. Magnetic Poles • The force exerted by a magnet on another object is strongest at the two poles of the object • Like magnetic poles repel. • Opposite magnetic poles attract • Most magnets have two poles (dipole), but can have three or more!

  9. Monopole (not Monopoly) • Monopole: piece of a magnet that is simply a north pole or a south pole • Many have tried to isolate a monopole by breaking magnets in half. • No matter how we break a magnet, the pieces are always dipoles! • A monopole cannot be isolated. • Do not pass GO. • Do not collect $200.

  10. Magnetic Fields • Travel from North to South OUTSIDE the magnet

  11. Magnetic Fields • From South to North INSIDE the magnet

  12. Compasses and magnets • A compass can be used to identify the North and South poles of a magnet.

  13. Magnetic Field lines are Continuous

  14. Magnetic Field Lines Never Cross • And always form closed loops (they loop through the inside of the magnet. In the South and out the North

  15. Magnetic Fields Between Bar Magnets

  16. Earth’s Magnetism • Magnetic Field has REVERSED direction about 300 x in the last 170 million years • The poles “Wander” • Magnetic and geographic poles are not the same. Declination is about 11.5° • What is strange about the picture?

  17. Earth’s Magnetism • Magnetic North & South poles are opposite geographic North & South poles and are not exactly in the same place (about 11.5 degrees “off”.

  18. The Earth’s Magnetic Field • A bit more complex than a magnet

  19. The earth’s magnetic field Shaped by the solar wind. Compressed near the sun and elongated on the other side.

  20. Electricity and Magnetism • When more than one charged particle moves in a common direction, what is formed? • A CURRENT! • The motion of the charges creates a magnetic field. In which direction does the magnetic field travel? Use the 1st right hand rule to figure this out.

  21. First Right Hand Rule • Thumb points in the direction of the current (RIGHT HAND ONLY). Fingers curl in the direction of the magnetic field • Note the compass readings. This is used for CURRENT carrying wire!

  22. All current carrying wires generate magnetic fields • Long, straight wire • magnetic field is cylindrical around the wire • Draw magnetic field lines as concentric circles • Loop of wire: • magnetic field forms rings around the wire & through the loop • Note the direction of current in and out and the magnetic field direction

  23. What about a coil of wire (many loops) • Coil of wire (Solenoid Coil): • Magnetic field of each loop adds together • Overall field looks like that of a bar magnet • Out one end of the coil, back in the other end

  24. Iron Core Solenoids • An iron core has the effect of multiplying greatly the magnetic field of a solenoid compared to an air core solenoid.

  25. Electromagnets • Electromagnets are solenoids which have an iron core. • The ferromagnetic property of the iron core causes the internal magnetic domains of the iron to line up with the magnetic field produced by the current in the solenoid. The effect is the multiplication of the magnetic field by factors of tens to even thousands.

  26. Electromagnet (Solenoid with solid core)

  27. Why do I care about a solenoid? • Solenoids are commonly used as starters in cars. Often when a vehicle's starter is malfunctioning the solenoid is the problem. • Solenoids are mainly used in cars as actuators. A solenoid will move a component a certain distance after electricity has been applied. • Another common usage in vehicles is as a relay. A solenoid closes a circuit when electricity is applied.

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