Chapter 22 - Electromagnetic Induction

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  • Chapter 22 - Electromagnetic Induction

    1. 1. Chapter 22Electromagnetic Induction
    2. 2. Learning OutcomesDeduce from Faraday’s experiments onelectromagnetic induction or other appropriateexperiments: (i) that a changing magnetic field can induce an e.m.f. in a circuit; (ii) that the direction of the induced e.m.f. opposes the change producing it; (iii) the factors affecting the magnitude of the induced e.m.f.
    3. 3. Learning Outcomes Describe a simple form of a.c. generator (rotating coil or rotating magnet) and the use of slip rings (where needed). Sketch a graph of voltage output against time for a simple a.c. generator. Describe the structure and principle of operation of a simple iron-cored transformer as used for voltage transformation.
    4. 4. Learning Outcomes Recall and apply the equations VP / VS = NP / NS and VPIP = VSIS to new situations or to solve related problems. Describe the energy loss in cables and deduce the advantages of high voltage transmission.
    5. 5. QuizIn the previous chapter, you have learnt that a current canproduce a magnetic field, is the reverse possible?Yes, it is possible.In this chapter you will learn that a magnetic field canproduce an electrical current.
    6. 6. 22.1 Electromagnetic Induction Faraday’s Iron Ring Experiment
    7. 7. Faraday’s Iron Ring Experiment When switch S was closed or opened, Faradays noticed that the compass needle deflected momentarily. (The deflection of the compass needle shows that there was a magnetic field present that was caused by a current flowing in wire PQ) However, the compass needle did not deflect when the switch was left closed or opened.
    8. 8. Faraday’s Iron Ring Experiment From the experiment, it was concluded that when the current in coil A was ,a was caused to . The current in B is called an .
    9. 9. Faraday’s Iron Ring Experiment From the experiment, it was concluded that when the current in coil A was switched on or off , a was caused to . The current in B is called an .
    10. 10. Faraday’s Iron Ring Experiment From the experiment, it was concluded that when the current in coil A was switched on or off , a current was caused to . The current in B is called an .
    11. 11. Faraday’s Iron Ring Experiment From the experiment, it was concluded that when the current in coil A was switched on or off , a current was caused to flow in coil B . The current in B is called an .
    12. 12. Faraday’s Iron Ring Experiment From the experiment, it was concluded that when the current in coil A was switched on or off , a current was caused to flow in coil B . The current in B is called an induced current .
    13. 13. Faraday’s Iron Ring Experiment The induced current in coil B arose only when there was a .
    14. 14. Faraday’s Iron Ring Experiment The induced current in coil B arose only when there change in the magnetic field in the ring was a linking the coil B .
    15. 15. Faraday’s Solenoid Experiment When the magnet is inserted into the solenoid, the galvanometer needle , indicating an through the solenoid.
    16. 16. Faraday’s Solenoid Experiment When the magnet is inserted into the solenoid, the galvanometer needle deflected momentarily to one direction , indicating an through the solenoid.
    17. 17. Faraday’s Solenoid Experiment When the magnet is inserted into the solenoid, the galvanometer needle deflected momentarily to one direction , indicating an induced current flowing in one direction through the solenoid.
    18. 18. Faraday’s Solenoid Experiment When the magnet is withdrawn into the solenoid, the galvanometer needle , indicating an through the solenoid.
    19. 19. Faraday’s Solenoid Experiment When the magnet is withdrawn into the solenoid, the galvanometer needle deflected momentarily in opposite direction , indicating an through the solenoid.
    20. 20. Faraday’s Solenoid Experiment When the magnet is withdrawn into the solenoid, the galvanometer needle deflected momentarily in opposite direction , indicating an induced current flowing in opposite direction through the solenoid.
    21. 21. Faraday’s Solenoid Experiment When the magnet is stationary (either inside or outside the solenoid), there will be .
    22. 22. Faraday’s Solenoid Experiment When the magnet is stationary (either inside or outside the solenoid), there will be no deflection in the galvanometer indicating induced current no flowing through the solenoid .
    23. 23. QUIZWhat do you think will happen if you(i) change the number of turns of wire in the coil(ii) change the strength of the magnet used(iii) change the speed at which the magnet is moving
    24. 24. 22.1 Electromagnetic Induction
    25. 25. 22.1 Electromagnetic Induction It was discovered that the magnitude of the induced e.m.f. depends on:
    26. 26. 22.1 Electromagnetic Induction It was discovered that the magnitude of the induced e.m.f. depends on:(a) number of turns in the solenoid
    27. 27. 22.1 Electromagnetic Induction It was discovered that the magnitude of the induced e.m.f. depends on:(a) number of turns in the solenoid(b) strength of magnet
    28. 28. 22.1 Electromagnetic Induction It was discovered that the magnitude of the induced e.m.f. depends on:(a) number of turns in the solenoid(b) strength of magnet(c) speed at which the magnet is inserted or withdraw from the solenoid
    29. 29. The Laws of Electromagnetic InductionFaraday’s Law of Induction:The e.m.f. (electromotive force) generatedin a conductor is .
    30. 30. The Laws of Electromagnetic InductionFaraday’s Law of Induction:The e.m.f. (electromotive force) generatedin a conductor is to the proportional rate of change of magnetic lines of force flux) linking the (magnetic circuit .
    31. 31. The Laws of Electromagnetic InductionLenz’s Law:The direction of the induced e.m.f is alwayssuch that .
    32. 32. The Laws of Electromagnetic InductionLenz’s Law:The direction of the induced e.m.f is alwayssuch that its magnetic effect opposes the motion or change producing it .
    33. 33. Demonstration of the twolaws of electromagnetism
    34. 34. Demonstration of the two lawsof electromagnetismApparatus: Copper wire coil of about 20 turns, sensitive centre-zerogalvanometer, bar magnet.
    35. 35. Demonstration of the two lawsof electromagnetismProcedures: 1. Connect the ends of the coil to a sensitive centre-zero galvanometer by means of long leads (i.e. connecting wires).
    36. 36. Demonstration of the two lawsof electromagnetismProcedures: 2. Move the S-pole of a permanent bar magnet into the coil and note any deflection on the galvanometer.
    37. 37. Demonstration of the two lawsof electromagnetismProcedures: 3. Once the bar magnet is inside the coil, hold it stationary and gain note any deflection on the a galvanometer.
    38. 38. Demonstration of the two lawsof electromagnetismProcedures: 4. Next, move the S-pole of the magnet out of the coil and note any deflection on the galvanometer.
    39. 39. Demonstration of the two lawsof electromagnetismProcedures: 5. Repeat steps 2 to 4 using the N-pole of the same bar magnet.
    40. 40. Demonstration of the two lawsof electromagnetism S N S-pole of magnet moving into the solenoid.
    41. 41. Demonstration of the two lawsof electromagnetism 1. Galvanometer shows a deflection to the left - induced current S N flowing through the circuit. S-pole of magnet moving into the solenoid.
    42. 42. Demonstration of the two lawsof electromagnetism 1. Galvanometer shows a deflection to the left - induced current S N flowing through the circuit. 2. The induced current S-pole of magnet shows that an induced moving into the solenoid. e.m.f. is generated in the circuit.
    43. 43. Demonstration of the two lawsof electromagnetism 3. The induced current on the right-hand side of the coil flows in clockwise S N direction. By lenz’s law, the direction of the induced current opposes the change producing it, S-pole of magnet hence a S-pole moving in moving into the solenoid. will induce a south pole so as to try to repel it away.
    44. 44. Demonstration of the two lawsof electromagnetism 3. The induced current on the right-hand side of the coil flows in clockwiseN S S N direction. By lenz’s law, the direction of the induced current opposes the change producing it, S-pole of magnet hence a S-pole moving in moving into the solenoid. will induce a south pole so as to try to repel it away.
    45. 45. Demonstration of the two lawsof electromagnetism S N Magnet remains stationary in the solenoid.
    46. 46. Demonstration of the two lawsof electromagnetism S N 1. Galvanometer shows no deflection - no current flowing through the circuit. Magnet remains stationary in the solenoid.
    47. 47. Demonstration of the two lawsof electromagnetism S N S-pole of magnet S-pole of magnet moving into the solenoid. moving out the solenoid.
    48. 48. Demonstration of the two lawsof electromagnetism 1. Galvanometer shows a deflection to the right - induced current S N flowing through the circuit. S-pole of magnet S-pole of magnet moving into the solenoid. moving out the solenoid.
    49. 49. Demonstration of the two lawsof electromagnetism 1. Galvanometer shows a deflection to the right - induced current S N flowing through the circuit. 2. The induced current S-pole of magnet S-pole of magnet shows that an induced moving into the solenoid. moving out the solenoid. e.m.f. is generated in the circuit.
    50. 50. Demonstration of the two lawsof electromagnetism 3. The induced current on the right-hand side of the coil flows in anti- S N clockwise direction. By lenz’s law, the direction of the induced current opposes the change S-pole of magnet S-pole of magnet producing it, hence a S- moving into the solenoid. moving out the solenoid. pole moving out will induce a north pole so as to try to attract it.
    51. 51. Demonstration of the two lawsof electromagnetism 3. The induced current on the right-hand side of the coil flows in anti-S N S N clockwise direction. By lenz’s law, the direction of the induced current opposes the change S-pole of magnet S-pole of magnet producing it, hence a S- moving into the solenoid. moving out the solenoid. pole moving out will induce a north pole so as to try to attract it.
    52. 52. Demonstration of the two lawsof electromagnetism N S S-pole of magnet N-pole of magnet moving into the solenoid.moving into the solenoid.
    53. 53. Demonstration of the two lawsof electromagnetism 1. Galvanometer shows a deflection to the right - induced current N S flowing through the circuit. S-pole of magnet N-pole of magnet moving into the solenoid.moving into the solenoid.
    54. 54. Demonstration of the two lawsof electromagnetism 1. Galvanometer shows a deflection to the right - induced current N S flowing through the circuit. 2. The induced current S-pole of magnet shows that an induced N-pole of magnet moving into the solenoid.moving into the solenoid. e.m.f. is generated in the circuit.
    55. 55. Demonstration of the two lawsof electromagnetism 3. The induced current on the right-hand side of the coil flows in anti- N S clockwise direction. By lenz’s law, the direction of the induced current opposes the change S-pole of magnet N-pole of magnet producing it, hence a N- moving into the solenoid.moving into the solenoid. pole moving in will induce a north pole so as to try to repel it away.
    56. 56. Demonstration of the two lawsof electromagnetism 3. The induced current on the right-hand side of the coil flows in anti-S NN S clockwise direction. By lenz’s law, the direction of the induced current opposes the change S-pole of magnet N-pole of magnet producing it, hence a N- moving into the solenoid.moving into the solenoid. pole moving in will induce a north pole so as to try to repel it away.
    57. 57. Demonstration of the two lawsof electromagnetism N S Magnet remains stationary in the solenoid.
    58. 58. Demonstration of the two lawsof electromagnetism N S 1. Galvanometer shows no deflection - no current flowing through the circuit. Magnet remains stationary in the solenoid.
    59. 59. Demonstration of the two lawsof electromagnetism N S S-pole of magnet N-pole of magnet moving into the solenoid.moving out the solenoid.
    60. 60. Demonstration of the two lawsof electromagnetism 1. Galvanometer shows a deflection to the left - induced current N S flowing through the circuit. S-pole of magnet N-pole of magnet moving into the solenoid.moving out the solenoid.
    61. 61. Demonstration of the two lawsof electromagnetism 1. Galvanometer shows a deflection to the left - induced current N S flowing through the circuit. 2. The induced current S-pole of magnet N-pole of magnet shows that an induced moving into the solenoid.moving out the solenoid. e.m.f. is generated in the circuit.
    62. 62. Demonstration of the two lawsof electromagnetism 3. The induced current on the right-hand side of the coil flows in clockwise N S direction. By lenz’s law, the direction of the induced current opposes the change producing it, S-pole of magnet N-pole of magnet hence a N-pole moving moving into the solenoid.moving out the solenoid. out will induce a south pole so as to try to attract it.
    63. 63. Demonstration of the two lawsof electromagnetism 3. The induced current on the right-hand side of the coil flows in clockwiseN S N S direction. By lenz’s law, the direction of the induced current opposes the change producing it, S-pole of magnet N-pole of magnet hence a N-pole moving moving into the solenoid.moving out the solenoid. out will induce a south pole so as to try to attract it.
    64. 64. Lenz’s Law and Conservation of Energy• By Lenz’s law, the direction of the induced current is such as to the change causing it.• When we move the magnet into the coil, we have to do in overcoming the between the like poles. Hence mechanical energy is transformed into as indicated by the induced current flowing in the circuit.
    65. 65. Lenz’s Law and Conservation of Energy• By Lenz’s law, the direction of the induced current is such as to oppose the change causing it. • When we move the magnet into the coil, we have to do in overcoming the between the like poles. Hence mechanical energy is transformed into as indicated by the induced current flowing in the circuit.
    66. 66. Lenz’s Law and Conservation of Energy• By Lenz’s law, the direction of the induced current is such as to oppose the change causing it. • When we move the magnet into the coil, we have to do work in overcoming the between the like poles. Hence mechanical energy is transformed into as indicated by the induced current flowing in the circuit.
    67. 67. Lenz’s Law and Conservation of Energy• By Lenz’s law, the direction of the induced current is such as to oppose the change causing it. • When we move the magnet into the coil, we have to do work in overcoming the repulsion force between the like poles. Hence mechanical energy is transformed into as indicated by the induced current flowing in the circuit.
    68. 68. Lenz’s Law and Conservation of Energy• By Lenz’s law, the direction of the induced current is such as to oppose the change causing it. • When we move the magnet into the coil, we have to do work in overcoming the repulsion force between the like poles. Hence mechanical energy is transformed into electrical energy as indicated by the induced current flowing in the circuit.
    69. 69. Lenz’s Law and Conservation of Energy• When we move the magnet out the coil, we have to do in overcoming the between the unlike poles. Hence mechanical energy is transformed into as indicated by the induced current flowing in the circuit.
    70. 70. Lenz’s Law and Conservation of Energy• When we move the magnet out the coil, we have to do work in overcoming the between the unlike poles. Hence mechanical energy is transformed into as indicated by the induced current flowing in the circuit.
    71. 71. Lenz’s Law and Conservation of Energy• When we move the magnet out the coil, we have to do work in overcoming the attraction force between the unlike poles. Hence mechanical energy is transformed into as indicated by the induced current flowing in the circuit.
    72. 72. Lenz’s Law and Conservation of Energy• When we move the magnet out the coil, we have to do work in overcoming the attraction force between the unlike poles. Hence mechanical energy is transformed into electrical energy as indicated by the induced current flowing in the circuit.
    73. 73. 22.2 Alternating Current Generators• The a.c. generator is an electromagnetic device, which transforms into .• The d.c. motor is an electromagnetic device, which transforms into .
    74. 74. 22.2 Alternating Current Generators• The a.c. generator is an electromagnetic device, which transforms kinetic energy (mechanical energy) into .• The d.c. motor is an electromagnetic device, which transforms into .
    75. 75. 22.2 Alternating Current Generators• The a.c. generator is an electromagnetic device, which transforms kinetic energy (mechanical energy) into electrical energy .• The d.c. motor is an electromagnetic device, which transforms into .
    76. 76. 22.2 Alternating Current Generators• The a.c. generator is an electromagnetic device, which transforms kinetic energy (mechanical energy) into electrical energy .• The d.c. motor is an electromagnetic device, which transforms electrical energy into .
    77. 77. 22.2 Alternating Current Generators• The a.c. generator is an electromagnetic device, which transforms kinetic energy (mechanical energy) into electrical energy .• The d.c. motor is an electromagnetic device, which transforms electrical energy into kinetic energy (mechanical energy) .
    78. 78. 22.2 Alternating Current Generators• An a.c. generator consists of a rectangular coil of wire that is mounted on an axle. By turning the axle, the coil is made to rotate between the poles of a permanent magnet.
    79. 79. 22.2 Alternating Current Generators• As the coil rotates, the and therefore between the ends of the coil.
    80. 80. 22.2 Alternating Current Generators• As the coil rotates, the coil cuts the magnetic field lines (magnetic field the through coil is changing) and therefore between the ends of the coil.
    81. 81. 22.2 Alternating Current Generators• As the coil rotates, the coil cuts the magnetic field lines (magnetic field the through coil is changing) and therefore induced current is between the ends of the coil.
    82. 82. 22.2 Alternating Current Generators• Note: the ends of the coil must be connected to an external circuit with an electrical load such as a resistor for the current to flow.)
    83. 83. 22.2 Alternating Current Generators• The slip rings allow the transfer of the induced in the rotating coil to the external circuit. D C C D N S N S A B B A Slip rings
    84. 84. 22.2 Alternating Current Generators• The slip rings allow the transfer of the alternating current induced in the rotating coil to the external circuit. D C C D N S N S A B B A Slip rings
    85. 85. 22.2 Alternating Current Generators• The carbon brushes provides the contact between the slip rings and the external circuit which prevents wear and tear of the rings. D C C D N S N S A B B A Slip rings
    86. 86. 22.2 Alternating Current Generators• When the coil is horizontal, • The rate at which the coil . • Hence the induced e.m.f. is the . B A e.m.f./V EO 0 time/s -– EO one revolution
    87. 87. 22.2 Alternating Current Generators• When the coil is horizontal, • The rate at which the coil the magnetic field cuts lines is the greatest . • Hence the induced e.m.f. is the . B A e.m.f./V EO 0 time/s -– EO one revolution
    88. 88. 22.2 Alternating Current Generators• When the coil is horizontal, • The rate at which the coil the magnetic field cuts lines is the greatest . • Hence the induced e.m.f. is the maximum induced e.m.f. . B A e.m.f./V EO 0 time/s -– EO one revolution
    89. 89. 22.2 Alternating Current Generators• When the coil is vertical, • The coil is moving parallel to the magnetic field lines, hence it is . • Hence the induced e.m.f. is the . B A e.m.f./V EO 0 time/s -– EO one revolution
    90. 90. 22.2 Alternating Current Generators• When the coil is vertical, • The coil is moving parallel to the magnetic field lines, hence it is not cutting the magnetic field lines . • Hence the induced e.m.f. is the . B A e.m.f./V EO 0 time/s -– EO one revolution
    91. 91. 22.2 Alternating Current Generators• When the coil is vertical, • The coil is moving parallel to the magnetic field lines, hence it is not cutting the magnetic field lines . • Hence the induced e.m.f. is the zero . B A e.m.f./V EO 0 time/s -– EO one revolution
    92. 92. 22.2 Alternating Current Generators• When the number of turns on the coil is doubled without changing the frequency of the rotation of the coil, • The maximum output voltage will . • The frequency of the changing of direction of current flow will . e.m.f./V 2EO EO 0 – EO time/s – 2EO previous output voltage
    93. 93. 22.2 Alternating Current Generators• When the number of turns on the coil is doubled without changing the frequency of the rotation of the coil, • The maximum output voltage will doubled . • The frequency of the changing of direction of current flow will . e.m.f./V 2EO EO 0 – EO time/s – 2EO previous output voltage
    94. 94. 22.2 Alternating Current Generators• When the number of turns on the coil is doubled without changing the frequency of the rotation of the coil, • The maximum output voltage will doubled . • The frequency of the changing of direction of current flow will remains constant . e.m.f./V 2EO EO 0 – EO time/s – 2EO previous output voltage
    95. 95. 22.2 Alternating Current Generators• When the number of turns on the coil is doubled without changing the frequency of the rotation of the coil, • The maximum output voltage will doubled . • The frequency of the changing of direction of current flow will remains constant . e.m.f./V 2EO EO 0 – EO time/s – 2EO previous output voltage
    96. 96. 22.2 Alternating Current Generators• When the frequency of the rotation of the coil is doubled without changing the number of turns on the coil, • The maximum output voltage will . • The frequency of the changing of direction of current flow will . (i.e. Period is .) e.m.f./V 2EO EO 0 – EO time/s – 2EO previous output voltage
    97. 97. 22.2 Alternating Current Generators• When the frequency of the rotation of the coil is doubled without changing the number of turns on the coil, • The maximum output voltage will doubled . • The frequency of the changing of direction of current flow will . (i.e. Period is .) e.m.f./V 2EO EO 0 – EO time/s – 2EO previous output voltage
    98. 98. 22.2 Alternating Current Generators• When the frequency of the rotation of the coil is doubled without changing the number of turns on the coil, • The maximum output voltage will doubled . • The frequency of the changing of direction of current flow will doubled . (i.e. Period is halved .) e.m.f./V 2EO EO 0 – EO time/s – 2EO previous output voltage
    99. 99. 22.2 Alternating Current Generators• When the frequency of the rotation of the coil is doubled without changing the number of turns on the coil, • The maximum output voltage will doubled . • The frequency of the changing of direction of current flow will doubled . (i.e. Period is halved .) e.m.f./V 2EO EO 0 – EO time/s – 2EO previous output voltage
    100. 100. 22.2 Alternating Current Generators
    101. 101. 22.2 Alternating Current Generators• The alternating voltage output of an a.c. generator increases with
    102. 102. 22.2 Alternating Current Generators• The alternating voltage output of an a.c. generator increases with • an increase in the number of turns of coil used.
    103. 103. 22.2 Alternating Current Generators• The alternating voltage output of an a.c. generator increases with • an increase in the number of turns of coil used. • an increase in the speed of rotation of the coil.
    104. 104. 22.2 Alternating Current Generators• The alternating voltage output of an a.c. generator increases with • an increase in the number of turns of coil used. • an increase in the speed of rotation of the coil. • a stronger magnet used.
    105. 105. 22.2 Alternating Current Generators• The alternating voltage output of an a.c. generator increases with • an increase in the number of turns of coil used. • an increase in the speed of rotation of the coil. • a stronger magnet used. • a soft iron core placed in the centre of the coil of wire.
    106. 106. Other A.C. Generators (Practical design)• To generate large currents (as in turbine in power stations), it is more practical and advantageous to keep the and to .• Hence instead of the coil cutting the magnetic field (discussed previously), now the magnetic field cuts the coil.• Using this method, we can do away with the which is prone to wear & tear and not capable of carrying large currents.
    107. 107. Other A.C. Generators (Practical design)• To generate large currents (as in turbine in power stations), it is more practical and advantageous to keep the fixed and to coil .• Hence instead of the coil cutting the magnetic field (discussed previously), now the magnetic field cuts the coil.• Using this method, we can do away with the which is prone to wear & tear and not capable of carrying large currents.
    108. 108. Other A.C. Generators (Practical design)• To generate large currents (as in turbine in power stations), it is more practical and advantageous to keep the fixed and to rotate the magnetic coil field (electromagnet/magnet) around the coil . • Hence instead of the coil cutting the magnetic field (discussed previously), now the magnetic field cuts the coil.• Using this method, we can do away with the which is prone to wear & tear and not capable of carrying large currents.
    109. 109. Other A.C. Generators (Practical design)• To generate large currents (as in turbine in power stations), it is more practical and advantageous to keep the fixed and to rotate the magnetic coil field (electromagnet/magnet) around the coil . • Hence instead of the coil cutting the magnetic field (discussed previously), now the magnetic field cuts the coil.• Using this method, we can do away with the slip rings and the carbon brushes which is prone to wear & tear and not capable of carrying large currents.
    110. 110. Other A.C. Generators
    111. 111. Fleming’s Right Hand Rule• When a straight wire is moved inside a magnetic field, a current is induced in the wire. ! Right!hand! !• Fleming’s Right Hand Rule (Dynamo rule) can be used to determine the in the wire.
    112. 112. Fleming’s Right Hand Rule• When a straight wire is moved inside a magnetic field, a current is induced in the wire. ! Right!hand! !• Fleming’s Right Hand Rule (Dynamo rule) can be used to determine the of the induced current direction in the wire.
    113. 113. 22.3 Transformer• A transformer is a device used to of an a.c. supply. • To change a at to a at or vice versa.
    114. 114. 22.3 Transformer• A transformer is a device used to vary the voltage output of an a.c. supply. • To change a at to a at or vice versa.
    115. 115. 22.3 Transformer• A transformer is a device used to vary the voltage output of an a.c. supply. • To change a low alternating voltage at high current to a high alternating voltage at low current or vice versa.
    116. 116. 22.3 Transformer• It is a useful electrical device that is essential for • from power stations to the consuming loads (households and factories). • for proper operation of electrical appliances such as the mains-operated television and record player.
    117. 117. 22.3 Transformer• It is a useful electrical device that is essential for • electrical power transmission from power stations to the consuming loads (households and factories). • for proper operation of electrical appliances such as the mains-operated television and record player.
    118. 118. 22.3 Transformer• It is a useful electrical device that is essential for • electrical power transmission from power stations to the consuming loads (households and factories). • regulating voltages for proper operation of electrical appliances such as the mains-operated television and record player.
    119. 119. Structure of a Closed-Core Transformer Circuit Symbol• It consists of a of wire and a of wire wound round a which consists of (this is to reduce heat loss due to induced eddy current).
    120. 120. Structure of a Closed-Core Transformer Circuit Symbol• It consists of a of wire and a of wire wound round a which consists of (this is to reduce heat loss due to induced eddy current).
    121. 121. Structure of a Closed-Core Transformer Circuit Symbol• It consists of a primary coil of wire and a secondary coil of wire wound round a laminated soft iron core which consists of thin sheets of soft-iron insulated from each other by a coat of lacquer (this is to reduce heat loss due to induced eddy current).
    122. 122. The Working Principle of Transformer• The transformer is based on , it transfer supplied from the to the by between the two coils.
    123. 123. The Working Principle of Transformer• The transformer is based on Faraday’s iron ring experiment , it transfer energy electrical supplied from the primary coil to the secondary coil by electromagnetic induction between the two coils.
    124. 124. The Working Principle of Transformer• At the primary coil, the sets up a in the secondary coil . (Note: the frequency of the alternating current in both the primary coil and the secondary coil is .)
    125. 125. The Working Principle of Transformer• At the primary coil, the applied alternating voltage sets up a changing magnetic field in the secondary coil induces an e.m.f. the which in secondary coil . (Note: the frequency of the alternating current in both the primary coil and the secondary coil is same .) the
    126. 126. The Working Principle of Transformer• A step-up transformer is one where the e.m.f in the primary coil is than the e.m.f. in the secondary coil. • The number of turns in the primary coil is than the secondary coil• A step-down transformer is one where the e.m.f in the primary coil is than the e.m.f. in the secondary coil. • The number of turns in the primary coil is than the secondary coil.
    127. 127. The Working Principle of Transformer• A step-up transformer is one where the e.m.f in the primary coil is smaller than the e.m.f. in the secondary coil. • The number of turns in the primary coil is than the secondary coil• A step-down transformer is one where the e.m.f in the primary coil is than the e.m.f. in the secondary coil. • The number of turns in the primary coil is than the secondary coil.
    128. 128. The Working Principle of Transformer• A step-up transformer is one where the e.m.f in the primary coil is smaller than the e.m.f. in the secondary coil. • The number of turns in the primary coil is lesser than the secondary coil• A step-down transformer is one where the e.m.f in the primary coil is than the e.m.f. in the secondary coil. • The number of turns in the primary coil is than the secondary coil.
    129. 129. The Working Principle of Transformer• A step-up transformer is one where the e.m.f in the primary coil is smaller than the e.m.f. in the secondary coil. • The number of turns in the primary coil is lesser than the secondary coil• A step-down transformer is one where the e.m.f in the primary coil is larger than the e.m.f. in the secondary coil. • The number of turns in the primary coil is than the secondary coil.
    130. 130. The Working Principle of Transformer• A step-up transformer is one where the e.m.f in the primary coil is smaller than the e.m.f. in the secondary coil. • The number of turns in the primary coil is lesser than the secondary coil• A step-down transformer is one where the e.m.f in the primary coil is larger than the e.m.f. in the secondary coil. greater • The number of turns in the primary coil is than the secondary coil.
    131. 131. The Working Principle of Transformer• The equation that relates the number of turns of coil and e.m.f. is shown in the formula below:
    132. 132. The Working Principle of Transformer• The equation that relates the number of turns of coil and e.m.f. is shown in the formula below: NP = VP NS VS NP = No. of turns of coil in primary coil NS = No. of turns of coil in secondary coil VP = Applied e.m.f. in primary coil VS = Induced e.m.f. in secondary coil
    133. 133. Power Transfer in a Transformer• For an ideal transformer (100% efficient), the power supplied to the primary coil is fully transferred to the secondary coil. By principle of Conservation of Energy,
    134. 134. Power Transfer in a Transformer• For an ideal transformer (100% efficient), the power supplied to the primary coil is fully transferred to the secondary coil. By principle of Conservation of Energy,Power in primary coil = Power in secondary coil
    135. 135. Power Transfer in a Transformer• For an ideal transformer (100% efficient), the power supplied to the primary coil is fully transferred to the secondary coil. By principle of Conservation of Energy,Power in primary coil = Power in secondary coil VP IP = VS IS
    136. 136. Power Transfer in a Transformer• For an ideal transformer (100% efficient), the power supplied to the primary coil is fully transferred to the secondary coil. By principle of Conservation of Energy,Power in primary coil = Power in secondary coil VP IP = VS IS VP = Applied e.m.f. in primary coil IP = Applied current in primary coil VS = Induced e.m.f. in secondary coil IS = Induced current in secondary coil
    137. 137. Power Transfer in a Transformer• However there is no ideal or 100% efficiency transformer as • in the form in the primary coil, secondary coil and soft iron coil. • There is a of . Not all the produced by the primary coil is to the secondary coil.
    138. 138. Power Transfer in a Transformer• However there is no ideal or 100% efficiency transformer as • Energy is lost in the form of heat in the primary coil, secondary coil and soft iron coil. • There is a of . Not all the produced by the primary coil is to the secondary coil.
    139. 139. Power Transfer in a Transformer• However there is no ideal or 100% efficiency transformer as • Energy is lost in the form of heat in the primary coil, secondary coil and soft iron coil. • There is a leakage of flux . Not all the magnetic magnetic flux produced by the primary coil is linked to the secondary coil.
    140. 140. Power Transfer in a Transformer• In order to increase the efficiency of a transformer, it should have • for primary and secondary coils so that the heating effect is reduced. • primary coil and secondary coils are of the soft iron core to reduce leakage of magnetic flux
    141. 141. Power Transfer in a Transformer• In order to increase the efficiency of a transformer, it should have • Low-resistance (thicker) copper wire for primary and secondary coils so that the heating effect is reduced. • primary coil and secondary coils are of the soft iron core to reduce leakage of magnetic flux
    142. 142. Power Transfer in a Transformer• In order to increase the efficiency of a transformer, it should have • Low-resistance (thicker) copper wire for primary and secondary coils so that the heating effect is reduced. • primary coil and secondary coils are wound on the same part of the soft iron core to reduce leakage of magnetic flux
    143. 143. Example 1An ideal transformer is used to step down the mains supplyfrom 240 V to 12 V to operate a lamp rated at 12 V, 60 W.(a) Write down the turns ratio of the transformer. (b) How many turns are on the secondary coil if the primary coil has 2400 turns?
    144. 144. Example 1An ideal transformer is used to step down the mains supplyfrom 240 V to 12 V to operate a lamp rated at 12 V, 60 W.(c) Calculate the current flowing in the lamp when it is working optimally.(d) Find the current flowing in the primary coil.
    145. 145. Example 1An ideal transformer is used to step down the mains supplyfrom 240 V to 12 V to operate a lamp rated at 12 V, 60 W.(e) For such transformer, the secondary coil is usually made of thick wire. Explain this.
    146. 146. Example 1An ideal transformer is used to step down the mains supplyfrom 240 V to 12 V to operate a lamp rated at 12 V, 60 W.(e) For such transformer, the secondary coil is usually made of thick wire. Explain this. This is to reduce the heat loss as resistance is low for a thick wire. (Or to increase the efficiency of the transformer as heat lost is reduced with a thick low resistance wire.)
    147. 147. Example 2A lamp labelled 5.0 V, 35 W is connected to a powersupply. When the lamp is in normal operation, its potentialdifference is 5.0 V. A step down transformer is connectedbetween a 240 V power supply and the bulb.Calculate the current flowing in the 240 V power supply.
    148. 148. Transmission of Electrical Power • Electrical energy generated in a power station is transmitted to consumers using . • However, is lost in the transmission cables in the form of as the cables have . • [The power loss in cables, P = .]! • 230 kV 25 kV 11 kV 230 V Power Step up Network of power Step down station transformer cables transformer
    149. 149. Transmission of Electrical Power • Electrical energy generated in a power station is transmission cable transmitted to consumers using . • However, is lost in the transmission cables in the form of as the cables have . • [The power loss in cables, P = .]! • 230 kV 25 kV 11 kV 230 V Power Step up Network of power Step down station transformer cables transformer
    150. 150. Transmission of Electrical Power • Electrical energy generated in a power station is transmission cable transmitted to consumers using . • However, energy is lost in the transmission cables in the form of heat as the cables have . resistance • [The power loss in cables, P = .]! • 230 kV 25 kV 11 kV 230 V Power Step up Network of power Step down station transformer cables transformer
    151. 151. Transmission of Electrical Power • Electrical energy generated in a power station is transmission cable transmitted to consumers using . • However, energy is lost in the transmission cables in the form of heat as the cables have . resistance • [The power loss in cables, P = I2 R .]! • 230 kV 25 kV 11 kV 230 V Power Step up Network of power Step down station transformer cables transformer
    152. 152. Transmission of Electrical Power • To minimize the lost of power due to heat, we can use cables which reduces the resistance but we will have to support very heavy cables and the construction cost is high. Hence the other solution is to in the transmission cables.! 230 kV 25 kV 11 kV 230 V Power Step up Network of power Step down station transformer cables transformer
    153. 153. Transmission of Electrical Power • To minimize the lost of power due to heat, we can use thick cables which reduces the resistance but we will have to support very heavy cables and the construction cost is high. Hence the other solution is to in the transmission cables.! 230 kV 25 kV 11 kV 230 V Power Step up Network of power Step down station transformer cables transformer
    154. 154. Transmission of Electrical Power • To minimize the lost of power due to heat, we can use thick cables which reduces the resistance but we will have to support very heavy cables and the construction cost is high. Hence the other solution is to transmit high voltage in the transmission cables. ! 230 kV 25 kV 11 kV 230 V Power Step up Network of power Step down station transformer cables transformer
    155. 155. Transmission of Electrical Power • The output a.c. voltage from the generator is by a so that the transmission current is . • The very high voltage is then by a before it is used in homes.! 230 kV 25 kV 11 kV 230 V Power Step up Network of power Step down station transformer cables transformer
    156. 156. Transmission of Electrical Power • The output a.c. voltage from the generator is step up by a so that the transmission current is . • The very high voltage is then by a before it is used in homes.! 230 kV 25 kV 11 kV 230 V Power Step up Network of power Step down station transformer cables transformer
    157. 157. Transmission of Electrical Power • The output a.c. voltage from the generator is step up by a step-up transformer so that the transmission current is . • The very high voltage is then by a before it is used in homes.! 230 kV 25 kV 11 kV 230 V Power Step up Network of power Step down station transformer cables transformer
    158. 158. Transmission of Electrical Power • The output a.c. voltage from the generator is step up by a step-up transformer so that the transmission current is kept low . • The very high voltage is then by a before it is used in homes.! 230 kV 25 kV 11 kV 230 V Power Step up Network of power Step down station transformer cables transformer
    159. 159. Transmission of Electrical Power • The output a.c. voltage from the generator is step up by a step-up transformer so that the transmission current is kept low . • The very high voltage is then step down by a before it is used in homes.! 230 kV 25 kV 11 kV 230 V Power Step up Network of power Step down station transformer cables transformer
    160. 160. Transmission of Electrical Power • The output a.c. voltage from the generator is step up by a step-up transformer so that the transmission current is kept low . • The very high voltage is then step down by a step-down transformer before it is used in homes. ! 230 kV 25 kV 11 kV 230 V Power Step up Network of power Step down station transformer cables transformer
    161. 161. Transmission of Electrical Power • Advantage of using a.c. voltage: It can be easily using a .(This is not possible by using d.c.) • Advantage of high voltage transmission: It in the transmission cables.! • 230 kV 25 kV 11 kV 230 V Power Step up Network of power Step down station transformer cables transformer
    162. 162. Transmission of Electrical Power • Advantage of using a.c. voltage: It can be step-up & step-down easily using a .(This is not possible by using d.c.) • Advantage of high voltage transmission: It in the transmission cables.! • 230 kV 25 kV 11 kV 230 V Power Step up Network of power Step down station transformer cables transformer
    163. 163. Transmission of Electrical Power • Advantage of using a.c. voltage: It can be step-up & step-down easily using a transformer .(This is not possible by using d.c.) • Advantage of high voltage transmission: It in the transmission cables.! • 230 kV 25 kV 11 kV 230 V Power Step up Network of power Step down station transformer cables transformer
    164. 164. Transmission of Electrical Power • Advantage of using a.c. voltage: It can be step-up & step-down easily using a transformer .(This is not possible by using d.c.) • Advantage of high voltage transmission: It reduces power loss in the transmission cables. ! • 230 kV 25 kV 11 kV 230 V Power Step up Network of power Step down station transformer cables transformer
    165. 165. Example 3The figure below shows a simple illustration of howelectrical power is transmitted from a power station to afactory. ! (step-down transformer) 24 kW 200 km Vs = 2 kV 10 kVThe power station transmits power of 24 kW at 10 kV tothe sub-station. At the substation, the voltage is steppeddown to Vs = 2 kV before this power is transmitted to thefactory for use.
    166. 166. Example 3 ! (step-down transformer) 24 kW 200 km Vs = 2 kV 10 kV(a) Calculate the current in the power cables between the power station and the sub-station.
    167. 167. Example 3 ! (step-down transformer) 24 kW 200 km Vs = 2 kV 10 kV(b) If the resistance of the power cables between the power station and the sub-station is 0.05 Ω for every 1 km of cable, calculate the potential drop across the power cables.
    168. 168. Example 3 ! (step-down transformer) 24 kW 200 km Vs = 2 kV 10 kV(c) Hence or otherwise calculate the power loss from the power station to the sub-station.
    169. 169. Example 3 ! (step-down transformer) 24 kW 200 km Vs = 2 kV 10 kV(d) Find the primary voltage of the transformer at the sub- station before it is stepped down to 2 kV.(e)
    170. 170. Example 3 ! (step-down transformer) 24 kW 200 km Vs = 2 kV 10 kV(e) What is the turns ratio of the transformer at the sub- station in order for the transformer to step-down the voltage to 2 kV?(f)
    171. 171. Example 3 ! (step-down transformer) 24 kW 200 km Vs = 2 kV 10 kV(f) Explain why electricity from the power station is transmitted at a high voltage.
    172. 172. Example 3 ! (step-down transformer) 24 kW 200 km Vs = 2 kV 10 kV(f) Explain why electricity from the power station is transmitted at a high voltage. This is to reduce power loss

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