1. Chapter 21 Magnetism

2. Lodestones Magnetite – attracted iron Magnetite – attracted iron  Observed by the ancient Greeks

3. Coins http://en.ucoin.net/catalog/ http://en.ucoin.net/catalog/ http://en.ucoin.net/catalog/

4. Magnetic Force Force that a magnet exerts on another magnet, on iron (or similar metal) or on moving charges. Force that a magnet exerts on another magnet, on iron (or similar metal) or on moving charges. Acts over a distance Acts over a distance  Pushing magnets together  Closer you get more force  Farther away less force felt

5. All Magnets have two _________ Poles

6. Magnetic Poles Magnetic poles: region where the magnet’s force is strongest Magnetic poles: region where the magnet’s force is strongest The end of a magnet that points north is called the north pole, and the end pointing south is the south pole. The end of a magnet that points north is called the north pole, and the end pointing south is the south pole. Like poles repel Like poles repel Opposite poles attract Opposite poles attract

7. Would these magnets attract or repel?

9. How can a magnet exert a force on something it is not touching? Magnetic Fields

10. A compass lines up with the Magnetic Field Lines

12. What is the shape of the magnetic field of a single bar magnet? N S

15. Strong Field Weak Field The closeness of field lines indicates the strength of the field

16. Magnetic Field Lines Leave from the North pole and enter the south pole. Leave from the North pole and enter the south pole. Where the lines are closer the field is stronger. Where the lines are closer the field is stronger.

17. What is the shape of the magnetic field between two unlike poles? N S N S

20. What is the shape of the magnetic field between two like poles? N S N S

23. Would this be any different? N S N S

24. What is the shape of the magnetic field of a horseshoe magnet? N S

27. What is the shape of the Earth’s magnetic field?

28. Are the magnetic and geographic poles in the same location?

30. The magnetic field reverses are random from 0.1million years to over 50million years. The last was 780000 years ago. How do we know? The magnetic field reverses are random from 0.1million years to over 50million years. The last was 780000 years ago. How do we know?

31. Magnetism

33. Evidence suggests that the earths magnetic field is caused by the movement of molten metals near the earths core Evidence suggests that the earths magnetic field is caused by the movement of molten metals near the earths core Changes in the flow of the molten metals inside the earth may cause the magnetic poles to move Changes in the flow of the molten metals inside the earth may cause the magnetic poles to move

34. Magnetism

37. Earth as a magnet A compass aligns with the earth’s magnetic north A compass aligns with the earth’s magnetic north The magnetic poles do not coincide with the geographic poles The magnetic poles do not coincide with the geographic poles This discrepancy between the two poles is called magnetic declination This discrepancy between the two poles is called magnetic declination

38. Magnetic Declination.

39. Note Pigeons have domain magnetite magnets in their skulls and that helps them navigate. Pigeons have domain magnetite magnets in their skulls and that helps them navigate. Bees also have magnetic materials in the abdomens. Bees also have magnetic materials in the abdomens.

40. Solar Wind

42. Aurora

48. Magnetic Effects The most visible effect of the earths magnetic field is a colorful light display, called an aurora The most visible effect of the earths magnetic field is a colorful light display, called an aurora Collisions between the charged particles and other particles in the upper atmosphere create glowing lights Collisions between the charged particles and other particles in the upper atmosphere create glowing lights

51. Magnetism and Electricity Considered a separate phenomenon until in 1820’s Danish professor Hans Christian Oersted found that when electric current passes through a wire it deflects a compass needle. Considered a separate phenomenon until in 1820’s Danish professor Hans Christian Oersted found that when electric current passes through a wire it deflects a compass needle.

53. The Nature of the Magnetic Field An electric charge is surrounded by an electric field. An electric charge is surrounded by an electric field. If an electric charge is moving, it is ALSO surrounded by a magnetic field. If an electric charge is moving, it is ALSO surrounded by a magnetic field.

54. What causes a magnetic field? A magnetic field is produced by the motion of electric charge. A magnetic field is produced by the motion of electric charge.

55. A magnet will not attract all objects or even all metal objects. Only a few metals, such as iron, cobalt, or nickel, are attracted to magnets or can be made into permanent magnets. What makes these elements magnetic? Magnetism

56. Spinning electrons in orbit around nucleus produce magnetic fields. Spinning electrons in orbit around nucleus produce magnetic fields.

57. Note Electrons spinning in opposite directions can cancel out the magnetic field. Electrons spinning in opposite directions can cancel out the magnetic field. The iron atom has 4 electrons whose spin does not cancel out. The iron atom has 4 electrons whose spin does not cancel out.

60. Ferromagnetic Materials Iron, Nickel, Cobalt Iron, Nickel, Cobalt They are strongly affected by magnetic fields. They are strongly affected by magnetic fields.

61. Paramagnetic Materials Paramagnetic materials include magnesium, molybdenum, lithium, and tantalum. Paramagnetic materials include magnesium, molybdenum, lithium, and tantalum. They are somewhat affected by magnetic fields. They are somewhat affected by magnetic fields.

62. Magnetic domains Iron atoms have a strong magnetic field Iron atoms have a strong magnetic field Groups of adjacent atoms line up with each other Groups of adjacent atoms line up with each other These clusters of aligned atoms are called magnetic domains These clusters of aligned atoms are called magnetic domains

63. Magnetic Domains A domain consists of billions of aligned atoms A domain consists of billions of aligned atoms Each domain is like a microscopic magnet Each domain is like a microscopic magnet

64. Iron becomes magnetized when the random domains rotate to become aligned Iron becomes magnetized when the random domains rotate to become aligned

66. Permanent Magnets Domains can be aligned by Domains can be aligned by Placing the iron in a strong magnetic field Placing the iron in a strong magnetic field Stroking the iron with a strong magnet Stroking the iron with a strong magnet

69. How can a magnet attract an iron nail The magnetic field of the magnet induces the domains in the nail to align. The magnetic field of the magnet induces the domains in the nail to align. The nail becomes a temporary magnet, The nail becomes a temporary magnet,

70. Magnetism Can a magnetic pole be isolated? Start breaking a magnet into smaller and smaller pieces

71. Go Past Domains

72. Magnetism What do you eventually get down to? A single atom

73. Magnetic poles can’t be separated from each other. Magnetic poles can’t be separated from each other. If you break a magnet in half each piece is still a magnet with a north and south pole. If you break a magnet in half each piece is still a magnet with a north and south pole. Ways to lose magnetism Ways to lose magnetism  Striking a magnet  Heating a Magnet

74. Diamagnetism Slight repulsion to magnets Slight repulsion to magnets Water – repelled slightly by a magnet Water – repelled slightly by a magnet Frog Levitation Frog Levitation

75. Frog Levitation

76. Hans Christian Oersted 1820

77. Electromagnetism Oersted’s Experiment

79. Electromagnetism A current carrying wire produces a circular magnetic field around itself.

81. The direction of the field can be predicted using a Right Hand Rule

82. Right Hand Rule

83. Electromagnetism What does the Field look like for a loop of wire?

84. Electromagnetism What does the Field look like for many loops of wire? (Coil or Solenoid)

85. Electromagnetism

87. Solenoid A coil of wire used to generate a nearly uniform magnetic field similar to that of a bar magnet. A coil of wire used to generate a nearly uniform magnetic field similar to that of a bar magnet. Has many practical applications. Has many practical applications.

88. Solenoids Each loop produces a magnetic field due to the current traveling through it. Each loop produces a magnetic field due to the current traveling through it. For solenoids with many loops, the magnetic field of each loop combine to produce a larger magnetic field For solenoids with many loops, the magnetic field of each loop combine to produce a larger magnetic field

90. If the solenoid is wrapped around an iron core, an electromagnet is formed. Electromagnetism

91. The solenoid’s magnetic field magnetizes the iron core. As a result, the field increases in strength.

92. Ways to Increase strength of an Electromagnet  Increase number of loops  Increase current  Use larger ferromagnetic core  Use soft iron core

93. Electromagnetism An electromagnet can be used to move large quantities of metal.

94. When a charge is moving in a magnetic field, the charge will be affected by the magnetic force. When a charge is moving in a magnetic field, the charge will be affected by the magnetic force. The right hand rule helps determine the direction of the force The right hand rule helps determine the direction of the force

95. Right Hand Rule For a positive test charge: Thumbdirection of motion of charge Fingers direction of magnetic field Out of palmdirection of magnetic force Force is perpendicular to the plane formed by the magnetic field and the direction of the motion of the charge.

96. Magnetic field Direction of motion of charge Magnetic Force

97. - When you placed a current-carrying wire in a magnetic field, the wire experiences a force. field, the wire experiences a force. - This force acts perpendicular to both the direction of the current and the direction of the magnetic field. current and the direction of the magnetic field.

98. Electromagnetic devices Turns electrical energy into mechanical energy (movement) Turns electrical energy into mechanical energy (movement) Electric Motors Electric Motors Loudspeakers Loudspeakers Galvanometers (ex. Gas Gauge) Galvanometers (ex. Gas Gauge)

99. Simple Galvanometer Used to detect small amounts of current Used to detect small amounts of current

100. Galvanometer

102. Motor

103. DC Motor

104. Electric Motors

105. Current in this arm flowing from left to right. Current in the same arm reverses, flowing from right to left. Current stops flowing momentarily in the coil but inertia will propel it to make contact once again, reversing the current in the coil.

106. Electromagnetism What happens if you move a wire in a magnetic field?

107. Electromagnetism You get a current in the wire

108. Generator A coil of wire is turned in a magnetic field generating a current.

109. http://micro.magnet.fsu.edu/electro mag/java/faraday2/ http://micro.magnet.fsu.edu/electro mag/java/faraday2/ http://micro.magnet.fsu.edu/electro mag/java/faraday2/ http://micro.magnet.fsu.edu/electro mag/java/faraday2/

110. Generator Devices for converting mechanical energy to electrical energy. Devices for converting mechanical energy to electrical energy. Spin a coil of wire through a magnetic field Spin a coil of wire through a magnetic field Will make a current flow through wire Will make a current flow through wire Makes alternating current as they go past the different poles of the magnet. Makes alternating current as they go past the different poles of the magnet.

113. Transformer Changes the voltage of alternating current Changes the voltage of alternating current Uses two coils of wire and a soft iron core Uses two coils of wire and a soft iron core Primary coil in Primary coil in Secondary coil out Secondary coil out AC currents must be used. AC currents must be used.

117. Step Up Transformers More loops on secondary coil More loops on secondary coil Increases Voltage Increases Voltage Decreases Current Decreases Current Power comes at high voltage because the power company loses less energy. (High current produces a lot of heat) Power comes at high voltage because the power company loses less energy. (High current produces a lot of heat)

118. Step Down Transformers Less loops on secondary coil Less loops on secondary coil Decreases Voltage Decreases Voltage Increases Current Increases Current Near your home Near your home A step-down transformer lowers the voltage to 120V or 240V for your house A step-down transformer lowers the voltage to 120V or 240V for your house

119. Transformers V 1  Primary wire’s voltage V 2  Secondary wire’s voltage N 1  number of loops in primary wire N 2  number of loops in secondary wire

120. Practice Problem In Egypt the voltage from a electrical plug is 220 V. Kareem wants to charge his Ipod from the US. He uses a transformer with a secondary coil of 300 turns. How many turns should the primary coil have? In Egypt the voltage from a electrical plug is 220 V. Kareem wants to charge his Ipod from the US. He uses a transformer with a secondary coil of 300 turns. How many turns should the primary coil have?

121. Transformers The power on both sides of the transformer has to be the same. (conservation of energy) And Since P = IV Combines to Give