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Unit #13: Magnetism

Unit #13: Magnetism. Adapted From Chin-Sung Lin, Eleanor Roosevelt High School, NYC. McNutt – 04/07/2014. Do Now 04/07/2014. Please complete the DN questions at the top of your guided notes using complete sentences. What do you know about magnetism?

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Unit #13: Magnetism

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  1. Unit #13:Magnetism Adapted From Chin-Sung Lin, Eleanor Roosevelt High School, NYC McNutt – 04/07/2014

  2. Do Now 04/07/2014 Please complete the DN questions at the top of your guided notes using complete sentences. What do you know about magnetism? What do you want to learn? What discoveries will be made and what projects will you create?

  3. History of Magnetism

  4. History The lodestone, which contains iron ore, was found more than 2000 years ago in the region of Magnesia in Greece

  5. History The earliest Chinese literature reference to magnetism lies in the 4th century BC writings Guiguzi (鬼谷子): "The lodestone attracts iron”

  6. History Zheng He used the Chinese compass as a navigational aid in his voyage between 1405 and 1433

  7. History In the 18th century, the French physicist Charles Coulomb studied the force between lodestones

  8. History In 1820 Danish physicist and chemist who discovered that electric currents create magnetic fields

  9. Historical Timeline Project We will dig deeper into important historical contributions on Wednesday. We will build a large-scale creative timeline along the back wall of our classroom.

  10. Magnetic Poles

  11. Magnetic Poles Magnets attract and repel without touching The interaction depends on the distance Magnetic poles produce magnetic forces

  12. Magnetic Poles Magnet can act as a compass The end that points northward is called north pole, and the end that points south is call the south pole

  13. Magnetic Poles All magnets have north and south poles They can never be separated from each other If you break the magnet in half, what will happen?

  14. Magnetic Poles Each half will become a complete magnet Unlike electric charge, you cannot have north or south pole alone

  15. Magnetic Poles Like poles repels; opposite poles attract

  16. Magnetic Fields

  17. Magnetic Fields The space around the magnet is filled with a magnetic field

  18. Magnetic Fields The magnetic field lines spread from the north pole to the south pole Where the lines are closer (at the poles), the field strength is stronger

  19. Magnetic Fields The magnetic field unit: Units: tesla (T) or gauss (G) 1 tesla = 10,000 gauss

  20. Magnetic Fields What will happen If we place a compass in the field?

  21. Magnetic Fields A magnet or small compass in the field will line up with the field

  22. Magnetic Fields Electric charge is surrounded by an electric filed The same charge is surrounded by a magnetic field if it is moving Which types of electron motion exist in magnetic materials?

  23. Magnetic Fields Electrons are in constant motion about atomic nuclei This moving charge constitutes a tiny current and produces a magnetic field

  24. Magnetic Fields Electrons spinning about their own axes constitute a charge in motion and thus creates another magnetic field Every spinning electron is a tiny magnet

  25. Magnetic Fields Electrons spinning in the same direction makes up a stronger magnet Spinning in opposite directions cancels out The field due to spinning is larger than the one due to orbital motion

  26. Magnetic Fields For ferromagnetic elements: iron, nickel, and cobalt, the fields do not cancel one another entirely Each iron atom is a tiny magnet

  27. Magnetic Domain

  28. Magnetic Domain Interactions among iron atoms cause large clusters of them to line up with one another These cluster of aligned atoms are called magnetic domains

  29. Magnetic Domain There are many magnetic domains in a crystal iron The difference between a piece of ordinary iron and an iron magnet is the alignment of domains

  30. Magnetic Domain Iron in a magnetic field: A growth in the size of the domains that is oriented in the direction of the magnetic field A rotation of domains as they are brought into alignment

  31. Magnetic Domain Permanent magnets: Place pieces of iron or certain iron alloys in strong magnetic fields Stroke a piece of iron with a magnet

  32. Electric Currents &Magnetic Fields

  33. Electric Currents & Magnetic Fields Current-Carrying Wire: A moving electron produces a magnetic field Electric current also produces magnetic field A current-carrying conductor is surrounded by a magnetic field

  34. Electric Currents & Magnetic Fields Right-hand rule: Grasp a current-carrying wire with your right hand Your thumb pointing to the direction of the current Your fingers would curl around the wire in the direction of the magnetic field (from N to S)

  35. Electric Currents & Magnetic Fields What will happen to the compasses if the current is upward? ?

  36. Electric Currents & Magnetic Fields The current-carrying wire deflects a magnetic compass

  37. Electric Currents & Magnetic Fields Current-Carrying Loop: A wire loop with current produces a magnetic field

  38. Electric Currents & Magnetic Fields Current-Carrying Loop: A wire loop with current produces a magnetic field

  39. Electric Currents & Magnetic Fields Coiled wire— Solenoid: A solenoid can be made of many wire loops

  40. Electric Currents & Magnetic Fields Coiled wire— Solenoid: A current-carrying coil of wire with many loops The magnetic field lines bunch inside the loop

  41. Electric Currents & Magnetic Fields Coiled wire— Solenoid: A coil wound into a tightly packed helix which produces a magnetic field when an electric current is passed through it Solenoids can create controlled magnetic fields and can be used as electromagnets

  42. Electric Currents & Magnetic Fields Intensity of Magnetic Field of Electromagnet (B): Increased as the number of loops increased (B ~ N) Increased as the Current increased (B ~ I) Intensity is enhanced by the iron core (B ~ μ) N B I

  43. Electric Currents & Magnetic Fields Permeability: The measure of the ability of a material to support the formation of a magnetic field within itself. Magnetic permeability is typically represented by the Greek letter μ μ B

  44. Electric Currents & Magnetic Fields Permeability:

  45. Electric Currents & Magnetic Fields • Direction of magnetic field of electromagnet follows the Right-hand Rule: • Your fingers indicate the direction of the current (I) • your thumb points the direction of the field (B) B I

  46. Magnetic Forces on Moving Charged Particles

  47. Magnetic Forces on Moving Charged Particles When a charged particle moves in a magnetic field, it will experience a deflecting force (FB) + I

  48. Magnetic Forces on Moving Charged Particles When a charged particle moves in a magnetic field, it will experience a deflecting force (FB) FB = qvB FB magnetic force [N] q electric charge [C] v velocity perpendicular to the field [m/s] B magnetic field strength [T, Teslas] I

  49. Magnetic Forces on Moving Charged Particles The magnetic field unit: Units: tesla (T) or gauss (G) 1 tesla = 10,000 gauss tesla = (newton × second)/(coulomb × meter) T = Ns / (Cm)

  50. Magnetic Forces on Moving Charged Particles Direction of the magnetic force (FB) follows the Fleming’s Left Hand Motor Rule I

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