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  1. 1. More free powerpoints at
  2. 2. Magnets have been known for centuries.The Chinese and Greeks knew about the“magical” properties of magnets. Theancient Greeks used a stone substancecalled “magnetite.” They discovered that thestone always pointed in the same direction.Later, stones of magnetite called“lodestones” were used in navigation.
  3. 3. William Gilbert, anEnglish physician,first proposed in1600 that the earthitself is a magnet,and he predicted thatthe Earth would befound to havemagnetic poles.
  4. 4. What is Magnetism? Magnetism is the force of attraction or repulsion of a magnetic material due to the arrangement of its atoms, particularly its electrons.
  5. 5. All magneticphenomena result from forces between electric charges in motion.
  6. 6. The ends of a magnet arewhere the magnetic effectis thestrongest. These arecalled “poles.” Eachmagnet has2 poles – 1 north, 1 south.
  7. 7. Like repels like…Opposites attract!
  8. 8. Poles of a magnet always Come in pairs!
  9. 9. If you cut a magnet in half, S N S N S Nyou get 2 magnets!
  10. 10. No Monopoles AllowedIt has not been shown to be possible to end up with a singleNorth pole or a single South pole, which is a monopole ("mono"means one or single, thus one pole).  S NNote: Some theorists believe that magnetic monopoles mayhave been made in the early Universe. So far, none have beendetected.
  11. 11. MagneticFields The region where the magnetic forces act is called the “magnetic field”
  12. 12. Defining Magnetic Field Direction Magnetic Field vectors as written as B Direction of magnetic field at any point is defined as the direction of motion of a charged particle on which the magnetic field would not exert a force. Magnitude of the B-vector is proportional to the force acting on the moving charge, magnitude of the moving charge, the magnitude of its velocity, and the angle between v and the B-field. Unit is the Tesla or the Gauss (1 T = 10,000 G).
  13. 13. Field Lines Around a Bar Magnet
  14. 14. Field Lines Around a Magnetic Sphere
  15. 15. Field Lines of Repelling Bars
  16. 16. Field Lines of Attracting Bars
  17. 17. Atoms themselves have magnetic properties due to the spin of the atom’s electrons.Groups of atoms join so that their magneticfieldsThese areas of atoms are direction are all going in the same called“domains”
  18. 18. When an unmagnetized substance is placed in a magnetic field, the substance can become magnetized. This happens when the spinning electrons line up in the same direction.
  19. 19. An unmagnetized substancelooks like this…
  20. 20. While a magnetized substance looklike this… Iron Lodestone (Magnetite)
  21. 21. How to break a magnet: 1. Drop it 2. Heat it This causes the domains to become random again!
  22. 22. Making and Breaking Magnets In most materials, if you add energy to the electrons, you can get them to move and realign Can you think of ways to add energy to electrons? How can you make a magnet? How can you demagnetize a magnet? What happens when you break a magnet?
  23. 23. Magnetic Field Vectors Due to a Bar Magnet N S
  24. 24. NS
  25. 25. NS
  26. 26. NS
  27. 27. NS
  28. 28. NS
  29. 29. NS
  30. 30. NS
  31. 31. NS
  32. 32. NS
  33. 33. Magnetic Field Lines• The direction of the magnetic field at any point is tangent to the magnetic field line at that point.
  34. 34. NS
  35. 35. Vocabulary for ELL• Magnet: material that can both attract and repel other magnets. Iron is most common.• Pole: Part of the magnet where the force is the strongest S N• Metal: material that is often attracted to magnets and a good electrical conductor• Horseshoe magnet:• U-shaped magnet
  36. 36. The Earth is a magnet:It exerts magneticforces and issurrounded by amagnetic fieldthat is strongestnear theNorth and Southmagnetic poles
  37. 37. Sometimes,the Earth’s Magnetic North Polemagneticpoles flip.This happensevery half-million yearsor so. Magnetic South Pole
  38. 38. We use the Earth’s magnetic field to find direction.The needle of a compass always pointstoward the magnetic south pole. We call this direction “North” (remember, opposites attract)
  39. 39. Vocabulary for ELLGeographic North pole: the north end of theaxis around which the Earth rotatesMagnetic North pole: the point on the Earthto which a compass needle points
  40. 40. The sun has a magnetic field, too.It extends far above the sun’ssurface. Other planets in the solar system also have these magnetic fields
  41. 41. When a charged particle enters amagnetic field, an electric force isexerted on it. If a charged particlemoves at an angle to a magnetic field,the magnetic force acting on it willcause it to move in a spiral around themagnetic field lines.
  42. 42. The solar wind is constantly bombardingthe Earth’s magnetic field. Sometimesthese charged particles penetrate thatfield. These particles are found in twolarge regions known as the Van AllenBelts.
  43. 43. The Earth’s magnetic field extendsfar into space. It is called the“magnetosphere.” When the magnetic particles from the sun, called “solar wind”, strike this magnetosphere, we see a phenomenon called…
  44. 44. The Aurora Borealis in the Northern Hemisphere And the Aurora Australis in the Southern Hemisphere
  45. 45. Electricity and Magnetism Electric forces hold atoms andmolecules together. Electricity controls our thinking, feeling,muscles and metabolic processes. Electricity and magnetism underpinmuch of our current technology (e.g.computers). Electricity and magnetism are linkedon a fundamental level.
  46. 46. Electric MotorAn electric motor, is amachine which convertselectrical energy intomechanical (rotational orkinetic) energy.A current is passedthrough a loop which isimmersed in a magneticfield. A force exists onthe top leg of the loopwhich pulls the loop outof the paper, while aforce on the bottom legof the loop pushes the The net effect of these forces isloop into the paper. to rotate the loop.
  47. 47. Electromagnet (Magnetism from Electricity) An electromagnet is simply a coil of wires which, when a current is passed through, generate a magnetic field, as below.
  48. 48. Magnetic Properties of MatterIn other words….materials which producemagnetic fields with no apparent circulation ofcharge.All substances - solid, gas, and liquid - react tothe presence of a magnetic field on some level.Remember why?How much they react causes them to be put intoseveral material “types”.
  49. 49. Top Ten List What We Will Learn About Magnetism1. There are North Poles and South Poles.2. Like poles repel, unlike poles attract.3. Magnetic forces attract only magnetic materials.4. Magnetic forces act at a distance.5. While magnetized, temporary magnets act like permanentmagnets.
  50. 50. Top Ten Continued9. A charged particle experiences no magnetic force whenmoving parallel to a magnetic field, but when it is movingperpendicular to the field it experiences a force perpendicularto both the field and the direction of motion.10. A current-carrying wire in a perpendicular magnetic fieldexperiences a force in a direction perpendicular to both thewire and the field.
  51. 51. Let’s Play!