1. © 2010 Pearson Education, Inc. Conceptual Physics 11 th Edition Chapter 22: ELECTROSTATICS

2. © 2010 Pearson Education, Inc. Chapter 22 Chapter Objectives Electrical Forces and Charges Conservation of Charge Coulomb’s Law Conductors and Insulators Charge Polarization Electric Field Electric Potential Electric Energy Storage Warm-Up If the electrons around an atom’s nucleus are spinning then why don’t they just fly off?

3. © 2010 Pearson Education, Inc.

4. Electricity= electrical phenomena At rest = electrostatics = ch 22 Electrical current “charges” = Ch 23 Current & magnetism = Ch 24 Using electricity and magnetism = Ch 25

5. © 2010 Pearson Education, Inc. When you brush your hair and scrape electrons from your hair, the charge of your hair is A.positive. B.negative. C.Both A and B. D.Neither A nor B. Electric Force and Charges CHECK YOUR NEIGHBOR

6. © 2010 Pearson Education, Inc. When you brush your hair and scrape electrons from your hair, the charge of your hair is A.positive. B.negative. C.Both A and B. D.Neither A nor B. Comment: And if electrons were scraped off the brush onto your hair, your hair would have a negative charge. Electric Force and Charges CHECK YOUR ANSWER

7. © 2010 Pearson Education, Inc. Coulomb’s Law Charge polarization Atom or molecule in which the charges are aligned with a slight excess of positive charge on one side and slight excess of negative charge on the other Example: Rub an inflated balloon on your hair and place the balloon on the wall. The balloon sticks to the wall due to charge polarization in the atoms or molecules of the wall.

8. © 2010 Pearson Education, Inc. Conservation of Charge Conservation of charge In any charging process, no electrons are created or destroyed. Electrons are simply transferred from one material to another. Tape demo

9. © 2010 Pearson Education, Inc. Coulomb’s Law Coulomb’s law This formula describes the transfer (electrical force) Differences between gravitational and electrical forces Electrical forces may be either attractive or repulsive. Gravitational forces are only attractive.

10. © 2010 Pearson Education, Inc. Coulomb’s Law Coulomb’s law (continued) If the charges are alike in sign, the force is repelling; if the charges are not alike, the force is attractive. In equation form: k = 9,000,000,000 Nm 2 /C 2 Unit of charge is coulomb, C Similar to Newton’s law of gravitation for masses Underlies the bonding forces between molecules

11. © 2010 Pearson Education, Inc. According to Coulomb’s law, a pair of particles that are placed twice as far apart will experience forces that are A.half as strong. B.one-quarter as strong. C.twice as strong. D.4 times as strong. Coulomb’s Law CHECK YOUR NEIGHBOR

12. © 2010 Pearson Education, Inc. According to Coulomb’s law, a pair of particles that are placed twice as far apart will experience forces that are A.half as strong. B.one-quarter as strong. C.twice as strong. D.4 times as strong. Practice Coulomb’s Law Worksheet Coulomb’s Law CHECK YOUR ANSWER

13. © 2010 Pearson Education, Inc. Chapter 22 Chapter Objectives Electrical Forces and Charges Conservation of Charge Coulomb’s Law Conductors and Insulators Charge Polarization Electric Field Electric Potential Electric Energy Storage Warm-Up Get out HW then answer the following Give an example of a conductive material. Give and example of an insulating material

14. © 2010 Pearson Education, Inc. Conductors and Insulators Conductor: Materials in which one or more of the electrons in the outer shell of its atoms are not anchored to the nuclei of particular atoms but are free to wander in the material –Example: Metals such as copper and aluminum Insulators: Materials in which electrons are tightly bound and belong to particular atoms and are not free to wander about among other atoms in the material, making them flow –Example: Rubber, glass

15. © 2010 Pearson Education, Inc. When you buy a water pipe in a hardware store, the water isn’t included. When you buy copper wire, electrons A.must be supplied by you, just as water must be supplied for a water pipe. B.are already in the wire. C.may fall out, which is why wires are insulated. D.None of the above. Conductors and Insulators CHECK YOUR NEIGHBOR

16. © 2010 Pearson Education, Inc. When you buy a water pipe in a hardware store, the water isn’t included. When you buy copper wire, electrons A.must be supplied by you, just as water must be supplied for a water pipe. B.are already in the wire. C.may fall out, which is why wires are insulated. D.None of the above. Conductors and Insulators CHECK YOUR ANSWER

17. © 2010 Pearson Education, Inc. Charging- Apply Electrical Charge by CONTACT Charging by friction and contact. Example: Stroking cats fur, combing your hair, rubbing your shoes on a carpet Electrons transfer from one material to another by simply touching. For example, –when a negatively charged rod is placed in contact with a neutral object, some electrons will move to the neutral object. –http://www.bing.com/videos/search?q=van+de+graaf+generator&&view=deta il&mid=B648FB2565AA7D565293B648FB2565AA7D565293&rvsmid=ABD0 6ACE3DE4C7CFF49CABD06ACE3DE4C7CFF49C&fsscr=0http://www.bing.com/videos/search?q=van+de+graaf+generator&&view=deta il&mid=B648FB2565AA7D565293B648FB2565AA7D565293&rvsmid=ABD0 6ACE3DE4C7CFF49CABD06ACE3DE4C7CFF49C&fsscr=0

18. © 2010 Pearson Education, Inc. Charging- Apply Electrical Charge by INDUCTION Induction: Consider two insulated metal spheres A and B. a.They touch each other, so in effect they form a single uncharged conductor. b.When a negatively charged rod is brought near A, electrons in the metal, being free to move, are repelled as far as possible until their mutual repulsion is big enough to balance the influence of the rod. The charge is redistributed. c.If A and B are separated while the rod is still present, each will be equal and oppositely charged.

19. © 2010 Pearson Education, Inc. Charging Charging by induction –If you bring a charged object near a conducting surface, electrons are made to move in the surface material, even without physical contact. –Example: The negative charge at the bottom of the cloud induces a positive charge on the buildings below.

20. © 2010 Pearson Education, Inc. Open up your book and work on the following problems Ranking page 400 1 and 2 Exercises page 401 8, 11, 13, 15, 19, 22, 23, 25, 28, 29, 33, 34, 35

21. © 2010 Pearson Education, Inc. Chapter 22 Chapter Objectives Electrical Forces and Charges Conservation of Charge Coulomb’s Law Conductors and Insulators Charge Polarization Electric Field Electric Potential Electric Energy Storage Warm-Up Get out HW We will check HW Review for Quiz Take the Quiz then have a lecture

22. © 2010 Pearson Education, Inc. Electric Field Electric field Space surrounding an electric charge (an energetic aura) Describes electric force Around a charged particle obeys inverse-square law Force per unit charge E= F/q

23. © 2010 Pearson Education, Inc. Electric Field Electric field direction Same direction as the force on a positive charge Opposite direction to the force on an electron- closer = stronger

24. © 2010 Pearson Education, Inc. Electric Field Both Lori and the spherical dome of the Van de Graaff generator are electrically charged.

25. © 2010 Pearson Education, Inc.

28. Electric Potential Electric potential (voltage) Energy per charge possessed by a charged particle due to its location May be called voltage—potential energy per charge In equation form: electric potential energy Electric potential  amount of charge

29. © 2010 Pearson Education, Inc. Electric Potential Electric potential (voltage) (continued) Unit of measurement: volt, Example: Twice the charge in same location has twice the electric potential energy but the same electric potential. 3 times the charge in same location has 3 times the electric potential energy but the same electric potential (2 E/2 q = 3 E/3 q = V) 1 volt  1 coulomb 1 joule

30. © 2010 Pearson Education, Inc. Electric potential energy is measured in joules. Electric potential, on the other hand (electric potential energy per charge), is measured A.in volts. B.in watts. C.in amperes. D.also in joules. Electric Potential CHECK YOUR NEIGHBOR

31. © 2010 Pearson Education, Inc. Electric potential energy is measured in joules. Electric potential, on the other hand (electric potential energy per charge), is measured A.in volts. B.in watts. C.in amperes. D.also in joules. Electric Potential CHECK YOUR ANSWER

32. © 2010 Pearson Education, Inc. Chapter 22 Chapter Objectives Electrical Forces and Charges Conservation of Charge Coulomb’s Law Conductors and Insulators Charge Polarization Electric Field Electric Potential Electric Energy Storage Warm-Up Finish lecture if needed Practice

33. © 2010 Pearson Education, Inc. Practice= CW NOT HW 1.Rev questions page 400 27 and 28 2.Exercises page 402 50-54 and 60 ( on pg 403) 3.Problems page 403 8 and 9 4.You and a partner will create 2 quiz questions. One conceptual question about the electric field and one math question about electric potential. We may use these on the next quiz so write good ones!

34. © 2010 Pearson Education, Inc. Chapter 23 Objective Flow of Charge Electric Current Voltage Sources Electrical Resistance Ohm’s Law Direct Current and Alternating Current Warm-Up- Look in your book 1.What type of device uses DC? 2.What type of device uses AC? 3.What type of current are the electric field lines around the earth?

35. © 2010 Pearson Education, Inc. Edison vs. Tesla- DC vs. AC current 1.Who was Thomas Edison and what is he given credit for invent? 2.Where did Edison have a summer home? 3.Did he REALLY invent this? 4.Who was Nikola Tesla and what many things did he invent? There are a few 5.What does DC and AC stand for? http://www.pbs.org/wgbh/amex/edison/sfeature/acdc.html http://www.pbs.org/wgbh/amex/edison/sfeature/acdc.html 6.Which type of current did Edison approve and what type of current did Tesla approve? 7.Was Tesla ever rich? 8.Did Tesla dress well? 9.Did the ladies like Tesla? 10.Did he like them back….?? 11.Why did cats and dogs start to disappear while Edison was “studying” AC current? Rap: http://blog.press.princeton.edu/2013/04/04/tesla-vs-edison-epic-rap-battle/ Elephant: http://www.bing.com/videos/search?q=edison+and+elephant+ac+current&view=detail& mid=8D30135B038BA48C76668D30135B038BA48C7666&first=0&FORM=NVPFVRhttp://www.bing.com/videos/search?q=edison+and+elephant+ac+current&view=detail& mid=8D30135B038BA48C76668D30135B038BA48C7666&first=0&FORM=NVPFVR... Comic: http://theoatmeal.com/comics/tesla Movie: https://www.youtube.com/watch?v=RB882PSnnJY

36. © 2010 Pearson Education, Inc. Chapter 23 Chapter Objectives Flow of Charge Electric Current Voltage Sources Electrical Resistance Ohm’s Law Direct Current and Alternating Current Warm-Up Review for Quiz Take the Quiz Complete WU then Lecture

37. © 2010 Pearson Education, Inc. Which of these statements is true? A.Electric current is a flow of electric charge. B.Electric current is stored in batteries. C.Both A and B are true. D.Neither A nor B are true. Electric Current

38. © 2010 Pearson Education, Inc. Which of these statements is true? A.Electric current is a flow of electric charge. B.Electric current is stored in batteries. C.Both A and B are true. D.Neither A nor B are true. Explanation: Voltage, not current, is stored in batteries. The voltage will produce a current in a connecting circuit. The battery moves electrons already in the wire, but not necessarily those in the battery. Electric Current

39. © 2010 Pearson Education, Inc. Flow of Charge When the ends of an electrical conductor are at different electric potentials—when there is a potential difference—charge flows from one end to the other. –Analogous to water flowing from higher pressure to lower pressure

40. © 2010 Pearson Education, Inc. Flow of Charge To attain a sustained flow of charge in a conductor, some arrangement must be provided to maintain a difference in potential while charge flows from one end to the other. –A continuous flow is possible if the difference in water levels—hence the difference in water pressures—is maintained with the use of a pump.

41. © 2010 Pearson Education, Inc. Electric Current Electric current Flow of charged particles –In metal wires Conduction electrons are charge carriers that are free to move throughout atomic lattice. Protons are bound within the nuclei of atoms. –In fluids Positive ions and electrons constitute electric charge flow.

42. © 2010 Pearson Education, Inc. Ohm’s Law Ohm’s law Relationship between voltage, current, and resistance States that the current in a circuit varies in direct proportion to the potential difference, or voltage, and inversely with the resistance

43. © 2010 Pearson Education, Inc. Ohm’s Law Ohm’s law (continued) In equation form: Example: For a constant resistance, current will be twice as much for twice the voltage. For twice the resistance and twice the voltage, current will be unchanged. Resistors Circuit elements that regulate current inside electrical devices. Current  resistance voltage

44. © 2010 Pearson Education, Inc. Ohm’s Law Electric shock Damaging effects of shock result from current passing through the body. Electric potential difference between one part of your body and another part depends on body condition and resistance, which can range from 100 ohms to 500,000 ohms.

45. © 2010 Pearson Education, Inc. When you double the voltage in a simple electric circuit, you double the A.current. B.resistance. C.Both A and B. D.Neither A nor B. Ohm’s Law CHECK YOUR NEIGHBOR

46. © 2010 Pearson Education, Inc. Current  resistance voltage When you double the voltage in a simple electric circuit, you double the A.current. B.resistance. C.Both A and B. D.Neither A nor B. Explanation: This is a straightforward application of Ohm’s law. Ohm’s Law CHECK YOUR ANSWER

47. © 2010 Pearson Education, Inc. Electric Circuits- R, I and V Circuits Connected in two common ways: –series forms a single pathway for electron flow between the terminals of the battery, generator, or wall outlet –parallel forms branches, each of which is a separate path for the flow of electrons

48. © 2010 Pearson Education, Inc. Electric Circuits- R=sum and I=same V=sum Series circuits Characteristics of series circuit 1. Electric current through a single pathway. 2. Total resistance to current is the sum of individual resistances. 3. Current is equal to the voltage supplied by the source divided by the total resistance of the circuit. I=V/R

49. © 2010 Pearson Education, Inc.

50. Electric Circuits Series circuits Characteristics of series circuit (continued): 4. The total voltage impressed across a series circuit divides among the individual electrical devices in the circuit so that the sum of the “voltage drops” across the resistance of each individual device is equal to the total voltage supplied by the source. 5. The voltage drop across each device are proportional to its resistance. 6. If one device fails, current in the entire circuit ceases.

51. © 2010 Pearson Education, Inc.

52. Electric Circuits- R= “sum” I=sum V=same Parallel circuits Characteristics of parallel circuit: 1. Voltage is the same across each device. 2. The total current in the circuit divides among the parallel branches. The amount of current in each branch is inversely proportional to the resistance of the branch. 3. The total current in the circuit equals the sum of the currents in its parallel branches.

53. © 2010 Pearson Education, Inc.

54. Electric Circuits Parallel circuits Characteristics of parallel circuit (continued): 4. As the number of parallel branches is increased, the overall resistance of the circuit is decreased. 5. A break in one path does not interrupt the flow of charge in the other paths.

55. © 2010 Pearson Education, Inc.

56. When two identical lamps in a circuit are connected in parallel, the total resistance is A.less than the resistance of either lamp. B.the same as the resistance of each lamp. C.less than the resistance of each lamp. D.None of the above. Electric Circuits CHECK YOUR NEIGHBOR

57. © 2010 Pearson Education, Inc. When two identical lamps in a circuit are connected in parallel, the total resistance is A.less than the resistance of either lamp. B.the same as the resistance of each lamp. C.less than the resistance of each lamp. D.None of the above. Explanation: Resistors in parallel are like extra lines at a checkout counter. More lines means less resistance, allowing for more flow. Electric Circuits CHECK YOUR ANSWER

58. © 2010 Pearson Education, Inc. Consider a lamp powered by a battery. Charge flows A.out of the battery and into the lamp. B.from the negative terminal to the positive terminal. C.with a slight time delay after closing the switch. D.through both the battery and the lamp. Electric Circuits CHECK YOUR NEIGHBOR

59. © 2010 Pearson Education, Inc. Consider a lamp powered by a battery. Charge flows A.out of the battery and into the lamp. B.from the negative terminal to the positive terminal. C.with a slight time delay after closing the switch. D.through both the battery and the lamp. Explanation: Remember, charge is already in all parts of the conducting circuit. The battery simply gets the charges moving. As much charge flows in the battery as outside. Therefore, charge flows through the entire circuit. Electric Circuits CHECK YOUR ANSWER

60. © 2010 Pearson Education, Inc. Ch 23 Practice Plug and Chug page 420 ALL (1-6) Ranking page 420 1, 2, 3 Exercises page 421 1, 2, 3, 8, 9, 26, 30, 31, 32, 33

61. © 2010 Pearson Education, Inc. Chapter 24 Objectives Magnetic Forces, Poles, Fields Magnetic Domains Electric Currents and Magnetic Fields Electromagnets Magnetic Force on Moving Charged Particles Magnetic Force on Current Carrying Wires Earth’s Magnetic Field Warm-Up Get out HW Magnetism is a Force, can you name any others?

62. © 2010 Pearson Education, Inc. Forces gravitational Electric- coulomb’s law- just charged particles Magnetic- motion of charged particles

63. © 2010 Pearson Education, Inc. A weak and strong magnet repel each other. The greater repelling force is by the A.stronger magnet. B.weaker magnet. C.Both the same. D.None of the above. Magnetic Poles CHECK YOUR NEIGHBOR

64. © 2010 Pearson Education, Inc. A weak and strong magnet repel each other. The greater repelling force is by the A.stronger magnet. B.weaker magnet. C.Both the same. D.None of the above. Explanation: Remember Newton’s third law! Magnetic Poles CHECK YOUR ANSWER

65. © 2010 Pearson Education, Inc. Magnetic Fields Magnetic fields Strength indicated by closeness of the lines –lines close together; strong magnetic field –lines farther apart; weak magnetic field

66. © 2010 Pearson Education, Inc. Magnetic Fields Magnetic fields (continued) Produced by two kinds of electron motion – electron spin main contributor to magnetism pair of electrons spinning in same direction creates a stronger magnet pair of electrons spinning in opposite direction cancels magnetic field of the other –electron revolution

67. © 2010 Pearson Education, Inc. http://video.nationalgeographic.com/video/news /norway-aurora-borealis-vin

68. © 2010 Pearson Education, Inc. The source of all magnetism is A.electrons rotating around an atomic nucleus. B.electrons spinning around internal axes. C.either or both A and B. D.tiny bits of iron. Magnetic Fields CHECK YOUR NEIGHBOR

69. © 2010 Pearson Education, Inc. The source of all magnetism is A.electrons rotating around an atomic nucleus. B.electrons spinning around internal axes. C.either or both A and B. D.tiny bits of iron. Magnetic Fields CHECK YOUR ANSWER

70. © 2010 Pearson Education, Inc. Where magnetic field lines are more dense, the field there is A.weaker. B.stronger. C.Both A and B. D.Neither A nor B. Magnetic Fields CHECK YOUR NEIGHBOR

71. © 2010 Pearson Education, Inc. Where magnetic field lines are more dense, the field there is A.weaker. B.stronger. C.Both A and B. D.Neither A nor B. Magnetic Fields CHECK YOUR ANSWER

72. © 2010 Pearson Education, Inc. Chapter 24 Objectives Magnetic Forces, Poles, Fields Magnetic Domains Electric Currents and Magnetic Fields Electromagnets Magnetic Force on Moving Charged Particles Magnetic Force on Current Carrying Wires Earth’s Magnetic Field Warm-Up 1. review 2. quiz 3. lecture 4. HW

73. © 2010 Pearson Education, Inc. Magnetic Domains Magnetic domains Magnetized clusters of aligned magnetic atoms Permanent magnets made by placing pieces of iron or similar magnetic materials in a strong magnetic field. stroking material with a magnet to align the domains.

74. © 2010 Pearson Education, Inc. Magnetic Domains Difference between permanent magnet and temporary magnet Permanent magnet –alignment of domains remains once external magnetic field is removed Temporary magnet –alignment of domains returns to random arrangement once external magnetic field is removed

75. © 2010 Pearson Education, Inc. Magnetic Domains

76. © 2010 Pearson Education, Inc. Electric Currents and Magnetic Fields Connection between electricity and magnetism Magnetic field forms a pattern of concentric circles around a current-carrying wire. When current reverses direction, the direction of the field lines reverse.

77. © 2010 Pearson Education, Inc. Electric Currents and Magnetic Fields

78. © 2010 Pearson Education, Inc. Electric Currents and Magnetic Fields Magnetic field intensity increases as the number of loops increase in a current-carrying coil temporary magnet.

79. © 2010 Pearson Education, Inc. Electric Currents and Magnetic Fields Electromagnet Iron bar placed in a current-carrying coil Most powerful—employs superconducting coils that eliminate the core Applications –control charged-particle beams in high-energy accelerators –lift automobiles and other iron objects –levitate and propel high-speed trains

80. © 2010 Pearson Education, Inc. An electromagnet can be made stronger by A.increasing the number of turns of wire. B.increasing the current in the coil. C.Both A and B. D.None of the above. Electric Currents and Magnetic Fields CHECK YOUR NEIGHBOR

81. © 2010 Pearson Education, Inc. An electromagnet can be made stronger by A.increasing the number of turns of wire. B.increasing the current in the coil. C.Both A and B. D.None of the above. HW: page 438 1, 2, 4, 9, 13, 24 Electric Currents and Magnetic Fields CHECK YOUR ANSWER

82. © 2010 Pearson Education, Inc. Chapter 25 Objective Electromagnetic Induction Faraday’s Law Generators and Alternating Current Power Production Power Transmission Warm-Up Get out HW We need to check it

83. © 2010 Pearson Education, Inc. Electromagnetic Induction Electromagnetic induction Discovered by Faraday and Henry Induces voltage by changing the magnetic field strength in a coil of wire

84. © 2010 Pearson Education, Inc. Electromagnetic Induction Electromagnetic induction (continued) Induced voltage can be increased by –increasing the number of loops of wire in a coil. –increasing the speed of the magnet entering and leaving the coil. Slow motion produces hardly any voltage. Rapid motion produces greater voltage.

85. © 2010 Pearson Education, Inc. Electromagnetic Induction Voltage is induced in the wire loop whether the magnetic field moves past the wire or the wire moves through the magnetic field.

86. © 2010 Pearson Education, Inc. Electromagnetic Induction When a magnet is plunged into a coil with twice as many loops as another, twice as much voltage is induced. If the magnet is plunged into a coil with 3 times as many loops, 3 times as much voltage is induced.

87. © 2010 Pearson Education, Inc. Faraday’s Law Faraday’s law States that the induced voltage in a coil is proportional to the number of loops, multiplied by the rate at which the magnetic field changes within those loops. Amount of current produced by electromagnetic induction is dependent on –resistance of the coil, –circuit that it connects, –induced voltage.

88. © 2010 Pearson Education, Inc. Faraday’s Law It is more difficult to push the magnet into a coil with many loops because the magnetic field of each current loop resists the motion of the magnet.

89. © 2010 Pearson Education, Inc. The resistance you feel when pushing a piece of iron into a coil involves A.repulsion by the magnetic field you produce. B.energy transfer between the iron and coil. C.Newton’s third law. D.resistance to domain alignment in the iron. Faraday’s Law CHECK YOUR NEIGHBOR

90. © 2010 Pearson Education, Inc. The resistance you feel when pushing a piece of iron into a coil involves A.repulsion by the magnetic field you produce. B.energy transfer between the iron and coil. C.Newton’s third law. D.resistance to domain alignment in the iron. Faraday’s Law CHECK YOUR ANSWER

91. © 2010 Pearson Education, Inc. More voltage is induced when a magnet is thrust into a coil A.more quickly. B.more slowly. C.Both A and B. D.Neither A nor B. Faraday’s Law CHECK YOUR NEIGHBOR

92. © 2010 Pearson Education, Inc. More voltage is induced when a magnet is thrust into a coil A.more quickly. B.more slowly. C.Both A and B. D.Neither A nor B. Faraday’s Law CHECK YOUR ANSWER

93. © 2010 Pearson Education, Inc. Not only is voltage induced when a magnet is thrust into a coil of wire but ___________ is also induced. A.current B.energy C.power D.None of the above. Faraday’s Law CHECK YOUR NEIGHBOR

94. © 2010 Pearson Education, Inc. Not only is voltage induced when a magnet is thrust into a coil of wire but ___________ is also induced. A.current B.energy C.power D.None of the above. Comment: Don’t say energy or power, which are conservation-of-energy no-no’s! Energy can be transferred but not created by induction. Faraday’s Law CHECK YOUR ANSWER

95. © 2010 Pearson Education, Inc. Generators and Alternating Current Generator Opposite of a motor Converts mechanical energy into electrical energy via coil motion Produces alternating voltage and current

96. © 2010 Pearson Education, Inc. Generators and Alternating Current The frequency of alternating voltage induced in a loop is equal to the frequency of the changing magnetic field within the loop.

97. © 2010 Pearson Education, Inc. Power Production Transformer Input coil of wire—the primary powered by ac voltage source Output coil of wire—the secondary connected to an external circuit

98. © 2010 Pearson Education, Inc. Power Production Transformer (continued) Both wound on a common iron core so that the magnetic field of the primary passes through the secondary Uses an alternating current and voltage in one coil to induce an alternating current and voltage in a second coil

99. © 2010 Pearson Education, Inc. Power Production Transformers can be step-up or step-down voltage. Step-up transformer –produces a greater voltage in the secondary than supplied by the primary –secondary has more turns in coil than the primary Step-down transformer –produces a smaller voltage in the secondary than supplied by the primary –secondary has less turns in coil than the primary

100. © 2010 Pearson Education, Inc. Power Production Transformer transfers energy from one coil to another. (continued) Example: voltage stepped up before leaving power station voltage stepped down for distribution near cities by cables that feed power to the grid voltage stepped down again before being supplied to businesses and consumers through substations

101. © 2010 Pearson Education, Inc. Power Transmission Almost all electric energy sold today is in the form of ac because of the ease with which it can be transformed from one voltage to another. Large currents in wires produce heat and energy losses, so power is transmitted great distances at high voltages and low currents. Power is generated at 25,000 V or less and is stepped up near the power station to as much as 750,000 V for long-distance transmission. It is then stepped down in stages at substations and distribution points to voltages needed in industrial applications (often 440 V or more) and for the home (240 and 120 V).

102. © 2010 Pearson Education, Inc. A step-up transformer in an electrical circuit can step up A.voltage. B.energy. C.Both A and B. D.Neither A nor B. Power Production CHECK YOUR NEIGHBOR

103. © 2010 Pearson Education, Inc. A step-up transformer in an electrical circuit can step up A.voltage. B.energy. C.Both A and B. D.Neither A nor B. Explanation: Stepping up energy is a conservation of energy no-no! Power Production CHECK YOUR ANSWER