2. Remember?  An electron is moving downward with a velocity, v, in a magnetic field directed within the page, determine direction of force.

3. Moving conductor  Conductors contain free electrons  So when a conductor moves downward, electron will experience a magnetic force pulling them to the left.  Lattice atoms on the right become positive…  There is a potential difference now

4. Moving conductor  E force produced wanting to push electrons to the right  Forces are now balanced and electrons will stop moving  What will happen if you connect a resistor to the metal conductor?

5. Moving conductor  E force produced wanting to push electrons to the right  Forces are now balanced and electrons will stop moving  What will happen if you connect a resistor to the metal conductor?  Current will flow from high to low potential ++++++ –––––– R R

6. Moving conductor  What did we define emf previously as?  Amount of chemical energy converted to electrical energy per unit charge ++++++ –––––– R R

7. Moving conductor  What did we define emf previously as?  Amount of chemical energy converted to electrical energy per unit charge  We don’t have chemical energy here!!!  Where does our energy come from here? ++++++ –––––– R R

8. Moving conductor  Which direction were we pushing this conductor?  Another force acting on conductor? ++++++ –––––– R R

9. Moving conductor  Which direction were we pushing this conductor?  Another force acting on conductor?  Yes magnetic force… which direction is it acting? ++++++ –––––– R R

10. Moving conductor  Which direction were we pushing this conductor?  Another force acting on conductor?  Yes magnetic force… which direction is it acting? – upward  So when you’re pushing it downward, what energy is it gaining? ++++++ –––––– R R Force applied Magnetic force

11. Moving conductor  Which direction were we pushing this conductor?  Another force acting on conductor?  Yes magnetic force… which direction is it acting? – upward  So when you’re pushing it downward, what energy is it gaining? – EPE  You are doing work  If forces are equal, conductor is moving at constant v. ++++++ –––––– R R Force applied Magnetic force

12. Moving conductor  EPE will be converted into heat  Energy is conserved  Now let’s define INDUCED EMF?  Amount of mechanical energy converted into electrical energy per unit charge. ++++++ –––––– R R Force applied Magnetic force

13. Calculating induced EMF  Maximum p.d. in conductor is when the magnetic force ON ELECTRON is equal to the electrical force – L

14. Calculating induced EMF  Maximum p.d. in conductor is when the magnetic force ON ELECTRON is equal to the electrical force  Electron will stop moving.. Therefore greatest p.d.  Equate equations – L

15. Induced EMF equation **** The induced EMF will be the same as p.d. across conductor

16. Question  If magnetic field not perpendicular to direction of motion… what will you do? v B

17. Question  If magnetic field not perpendicular to direction of motion… what will you do?  Take the B that is perpendicular to v

18. Flemings right hand rule  FOR INDUCED CURRENT

19. QUESTION

21. THREE HAND RULES RIGHTLEFT

22. Faraday’s law  What generated induced emf?  What did it depend on?

23. Faraday’s law  What generated induced emf? – moving conductor in a magnetic field  What did it depend on?  Faraday’s law:  The induced emf is equal to the rate of change of flux

24. Flux VS flux density  Let’s look at this analogy

25. Flux VS flux density  How much grass do you have?  Is it taking lots of area?

26. Flux VS flux density  Pieces of grass is flux density (B)  Area over which grass takes over is flux (Φ)

27. Flux VS flux density Flux unit: Tm 2, Wb

28. Flux VS flux density Normal to surface  If area at angle from B  Find component of B that will be perpendicular to area θ

29. Lenz’s law  Moving conductor in magnetic field causes a force to oppose the direction of motion as seen earlier (if not true than energy will not be conserved)  Lenz’s law is an extension to Faraday by stating that:  the induced current will be in such a direction as to OPPOSE THE CHANGE IN FLUX that created the current.

30. Question

32.  Determine direction of current

33. Question

37.  Rail gun… how does it work? resistor

38. Question  What will happen if you remove the magnetic field suddenly? resistor

39. Question  BRING BACK THE FIIIEEEELLLDDD!!! LENZ’S LAW resistor

40. Question  to get the field back, which direction should the induced current be? resistor

41. Question  Current upward…. Force???? resistor

42. Question  Current upward…. Force to the right… and off it goes….. resistor

43. Question

44. http://science.howstuffworks.com/rail-gun1.htm

45. Read  Applications of EM induction on page 213

46. Alternating current (AC)  What’s the difference between a motor and a generator?

47. Alternating current (AC)  What’s the difference between a motor and a generator?  Motor  electrical to mechanical energy  Generator  mechanical to electrical

48. Alternating current (AC)  What’s the direction of current induced here?

49. Alternating current (AC)  What’s the flux going to be at angle 0?

50. Alternating current (AC)  What’s the flux going to be at angle 0?  Maximum since  So how will the graph look like?

51. Alternating current (AC) Label the positions in graph

52. Alternating current  Since we have many loops here we change the equation a bit and add “N” so that the total flux (called flux linkage):  Can we substitute θ with something else?

53. Alternating current ..

54. Alternating current (AC)  How will the emf graph with time look like?  What’s the emf equation?

55. Alternating current (AC)  How will the emf graph with time look like?  What’s the emf equation?  How can we get this value from the flux vs time graph?

56. Alternating current (AC)  How will the emf graph with time look like?  What’s the emf equation?  How can we get this value from the flux vs time graph? ---- (negative the gradient)

57. Alternating current (AC)

58.  So will the equation for emf have a sin or cos?

59. Alternating current (AC)  So will the equation for emf have a sin or cos?  Therefore at 90 degrees the emf in max and the flux is zero.

60. Alternating current (AC)

61. Emf and time  Emf vs time graph… what will happen if you double the angular speed…

62. Emf and time  Emf vs time graph… what will happen if you double the angular speed…  Double emf and half the period

63. Current and time  How can the current in the circuit be found?

64. Current and time  How can the current in the circuit be found?  ε 0 is equal to:  Can you think from where this equation came from?

65. Graphs

66. Definitions  AC: current delivered by rotating coil changing in direction and size over period of time  DC: constant current delivered from battery

67. question

68. Answer

69. Power  Equation(s)?

70. Power  P=IV, let substitute…  always positive

71. Power  Average power is about 50W in example below… how about the average current and voltage from previous graphs?

72. Power  Average power is about 50W in example below… how about the average current and voltage from previous graphs?  ZERO????  How do we solve this?

73. RMS  To solve this by calculating the root mean square (rms)  Square voltage or current then divide by two then square root the answer

74. Question

76. Power loss  Power transmitted through wire will be lost due to what factors?

77. Power loss  Power transmitted through wire will be lost due to what factors?  P= I 2 R [power loss to heating]  To reduce heat loss we have to reduce I  Reducing current, if DC was transmitted through power lines that feed homes, will have nothing left to run instruments..  AC, on the other hand, keeps on changing current and voltage…

78. Power loss  P=IV  So if we increased V then I will decrease since power supply in constant  So if we increase voltage by 100V, then the current will be less ( I /100)  So the power loss will be reduced by 100 2 (P= I 2 R)  WOW very useful and can only happen in AC  Ok… how can we do this? Transformers

79. Transformers  NO! Not the movie :p

80. Transformer  Current runs through primary.. What will it generate? iron

81. Transformer  Current runs through primary.. What will it generate? iron

82. Transformer  Current runs through primary.. What will it generate?  A magnetic field will be generated in all iron (that’s why it has to be a magnetic metal)  Now there is a magnetic field in in secondary coil.. What will happen? iron

83. Transformer  Current runs through primary.. What will it generate?  A magnetic field will be generated in all iron (that’s why it has to be a magnetic metal)  Now there is a magnetic field in in secondary coil.. What will happen? NOTHING  How can we make a current run through the secondary coil? iron

84. Transformer  Current runs through primary.. What will it generate?  A magnetic field will be generated in all iron (that’s why it has to be a magnetic metal)  Now there is a magnetic field in in secondary coil.. What will happen? NOTHING  How can we make a current run through the secondary coil? CHANGE THE FLUX – INDUCED EMF iron

85. Transformer  CHANGE IN FLUX created a current  Potential difference in primary coil is proportional to number of loops  so iron

86. Transformer  So lets look at the example above  Number of loops in secondary is greater than primary  So voltage in secondary will also be larger than primary  So how about the current? iron

87. Transformer  Look at above equation  Since voltage is more than the current will be less (since the power is constant).  So we just have MORE VOLTAGE (10/5 so double voltage) :D  Step up transformer iron

88. Transformer  Step up transformer to transport from plant to houses  Step down transformer at home to devices iron

89. Transformer

90. Question

91. answer

93. Read  For more information 218 and 219