5 The Law of PolesLike poles repel, unlike poles attract.
6 Can a magnet have only one pole? NoCan a magnet have more than two poles?Yes
7 Effects of Cutting?If a magnet is cut in half, lengthwise, will the two halves attract or repel?RepelIf a magnet is cut in half, across the width, will the two halves attract or repel?Attract36-2
8 Magnetic InductionMagnetism may be induced in iron and other materials.Stroking with a permanent magnetHeating and then cooling in a strong magnetic field
9 Natural Magnets Magnetite (lodestone) A naturally occurring magnetic materialProduced by heating and then cooling in the earth’s magnetic field
10 Soft Magnetic Materials IronEasily magnetizedWeakens quickly
11 Hard Magnetic Materials Cobalt and nickelDifficult to magnetizeStays strong longer
12 Magnetic Fields All charges are surrounded by an electric field. Charges in motion are surrounded by a magnetic field.
13 Magnet Fields Magnitude (strength) Direction Field descriptions must include:Magnitude (strength)DirectionThe direction that an isolated north pole would move when placed in the field19.2, 192
14 Magnetic Field LinesMagnetic field lines can be shown by using small iron filings79
15 Magnetic Field Of The Earth North-seeking and south seeking polesCompassesGeographic poles vs. magnetic polesLocation (north magnetic is in Canada)Dip angleMagnetic declinationThe angle between true north and magnetic north19.4
16 What is believed to be the source of the earth’s magnetic field? The earth’s magnetic field reverses every few million yearsEvidence?
17 Animals and MagnetismSome animals use the earth’s magnetic field for navigation.Anaerobic bacteriaLobstersBirds
18 Magnetic ForcesA charge experiences a force when moving through a magnetic field.Maximum force occurs when the motion is perpendicular to the field.Zero force occurs when the motion is parallel or antiparallel to the field.19.5
19 Factors Influencing Magnetic Force Which factors will determine the magnitude of the force on a charge that is moving through a magnetic field?Magnetic field strengthQuantity of chargeVelocity of the chargeDirection of the velocity
20 Magnetic Symbols New Symbols Formula Magnetic force (F) Magnetic field strength (B)Angle (q) (measured between v and B)Formula
21 Magnetic Field Strength Magnetic field strength unitsSITesla (T) or (1 Wb/m2)
22 Magnetic ForceFormulaRight Hand Rule19.6/19.7, 198
23 Magnetic Force On A Current Carrying-Conductor A current-carrying wire will experience a force when placed in a magnetic field.Symbols for current directionHeadTail26
25 Magnetic Force On A Straight Wire FormulaThere is no force when the current in the wire is in the same or opposite direction of the field.
26 Magnetic Force Applications Stereo speakerVoice coilElectromagnetic pumpNo moving partsPossible heart replacementMagnetohydrodynamic propulsion (MHD)199
27 Torque On A Current Loop A torque is exerted on a current-carrying loop when it is placed in a magnetic fieldApplicationsGalvanometersMotorsGenerators19.15, 19.17, 200, 201
28 Torque formula Shape of coil is not important Angle (q) is measured between B and the axis of the coilNumber of Turns (N)
29 Motion Of A Charged Particle In A Magnetic Field If the velocity is perpendicular to the field, the magnetic force is always toward the center of the circular path.Centripetal accelerationNo change in speedDirection change195, 80, 19.19
30 Curved Motion in a Magnetic Field Radius of curvature formula:197
32 Electricity and Magnetism Oersted lectureAn electric field deflected a nearby compass needleThis was the first realization of a link between electricity and magnetism
33 Magnetic Field Of A Long Straight Wire Oersted demonstrationCompasses surrounding a current-carrying wireThe magnetic field lines form circles around the wire.19.23a,b
34 Another Right-Hand Rule The Right-Hand-Rule for a currentIndicates the directions for current, magnetic field , and force19.23a
35 Magnetic Field Strength Formula for the magnetic field strength due to a current in a long straight wiremo is the permeability of free spacemo = 4p x 10-7 T.m/A
36 Magnetic Force Between Two Parallel Conductors Two parallel current-carrying conductors will exert a force on each other. (very important)19.28
37 Defining The Ampere Definition of the Ampere (1 A) Two long parallel wiresOne meter apartSame current in eachForce/length = 2 x 10-7 N/mRemember:1 Ampere = 1 Coulomb/second
38 Magnetic Field Of A Current Loop A current loop can increase the strength of the magnetic field.Current loops have poles.203, 19.28, 19.31
39 Magnetic Field Of A Solenoid A solenoid is made up of several closely spaced loops.Electromagnets are solenoidsApplicationsSolenoids have polesField lines are nearly parallel within204, 19.33, 19.32, 158, 159, 207
40 Formula for the magnetic field of a solenoid: n = N/L
41 Causes of Magnetism Orbital motion produces magnetic fields. These fields tend to cancel out.
42 Electron spin produces magnetic fields In most substances, electron pairs have opposite spins which cancel.Not in iron, nickel and cobalt
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