Ch 8 Notes

  1. Magnetism
  2. Magnets
  3. Magnetism – properties and interactions of magnets
  4. Magnetic Force – interaction between two magnets
  5. magnets exert a force on only some metals (iron, cobalt, and nickel) and each other
  6. Magnetic force increases as magnets move closer together
  7. Magnetic Field
  8. magnetic fields around magnets exerts a magnetic force
  9. strongest closest to magnet
  10. Magnetic Poles-where magnetic force is the strongest
  11. magnets have north and south poles
  12. poles at opposite ends of a bar magnet
  13. North pole of magnet points north when freely turning (compass)
  14. Magnetic field lines connect north and south poles
  15. Magnet Interaction
  16. can attract or repel
  17. opposites attract (North and South)
  18. likes repel (South/South and North/North)
  19. Magnetic fields combine to produce a new magnetic field
  20. Compass Needle
  21. magnet free to rotate can turn when placed into a magnetic field
  22. Compass has a small bar magnet that rotates
  23. North pole of compass will point towards south pole of bar magnet
  24. Compass needle will also line up along magnetic field lines that pass near it
  25. Earth’s Magnetic Field
  26. Earth acts like a giant bar magnet
  27. North pole of compass needle points north
  28. On Earth, its south magnetic pole is near its geographic north pole
  29. One theory says that the Earth’s magnetic field is caused by circulation of molten iron and nickel in the Earth’s core
  30. Electricity & Magnetism
  31. Electric Current and Magnetism
  32. Electricity and magnetism are related
  33. passing an electric current through a wire creates a circular magnetic field around the wire
  34. the direction of the field depends on the direction of the current
  35. the strength of the field depends on the amount of current flowing
  36. Electromagnets
  37. Electromagnet – a temporary magnet made by placing a piece of iron inside a coil or wire carrying a current
  38. Current flows through the loop of wire and magnetic field lines are produced
  39. If more loops are added, the field lines overlap and become stronger
  40. If an iron core is inserted into the coil, the iron becomes magnetized
  41. Properties of Electromagnets
  42. They are temporary magnets
  43. Has a north and south pole
  44. Aligns itself along magnetic field lines
  45. Is attracted or repelled by other magnets
  46. Magnetic properties can be controlled by changing the current
  47. Used in stereo speakers and electric motors and to lift large metal objects
  48. Electric motors
  49. Electric motor – a device that changes electrical energy into mechanical energy
  50. contains an electromagnet that is free to rotate between the poles of a permanent fixed magnet
  51. the coil is connected to a source of electric current (battery)
  52. current flows and a magnetic field is produced
  53. the functions of switching poles:
  54. coil in an electric motor turn so its north and south poles are aligned along the magnetic field lines of the permanent magnets (at opposite sides)
  55. once aligned, the coil will no longer rotate
  56. electric current in the coil is reversed and the like poles will be next to each other, and the coil will rotate (repel)
  57. a commutator or alternating current (AC) continuously reverses the current to keep the motor rotating
  58. more current – coil turns faster
  59. Producing Electric Current
  60. Mechanical to Electrical Energy
  61. Moving a magnet through a loop of wire produces a current
  62. Electromagnetic induction – moving a loop of wire through a magnetic field produces a current
  63. generators – produce electric current by electromagnetic induction
  64. works like an electric motor
  65. coil continuously turns as current switches direction, changes twice with each revolution and can be controlled
  66. Alternators – type of generator used in cars to provide energy to operate lights and other accessories
  67. Power Plants have huge generators where the magnets move instead of the coil
  68. Turbine – a large wheel that rotates when pushed by water, wind, or steam that is connected to rotating magnets
  69. Thermal energy (burning fossil fuels, steam) →mechanical energy (turbine blades move) →electrical energy (electrical current)
  70. Direct and Alternating Current
  71. Direct Current – flows in one direction through a wire (ex: battery)
  72. Alternating Current – reverses the direction of current flow in a regular way (ex: generator)
  73. Transformers
  74. Transformer – a device that increases or decreases the voltage of an alternating current
  75. made of two coils, primary and secondary, wrapped around an iron core
  76. if second coil has more turns than primary – increases voltage (step-up transformer)
  77. if second coil has less turns than primary – decreases voltage (step-down transformer)
  78. if secondary coil has two times more turns, then voltage would be doubled and vice versa
  79. Some energy carried by the current is lost as heat
  80. caused by resistance
  81. increases as wire increases in length
  82. power plants can lose up to 10% of their energy
  83. prevented by using higher voltages
  84. power lines – 750,000 volts
  85. homes – 120 volt (uses transformers)