PHY 2054 Magnetism - IThis Magnetic WeekWELCOME BACKHow Did You Do??Did the Card Help?Magnetism was known long ago.Lodestone (Mineral)New ConceptMagnetismWhere is Magnetism Used??And in magnets!!Compare to ElectrostaticsSlide 13MagnetsObservationsSlide 16Consider a Permanent MagnetIntroduce Another Permanent MagnetField of a Permanent MagnetSlide 20Electric field of an electric dipoleIron filings will align as a compass does –Examples of Creating Magnetic fieldsConvention For Magnetic FieldsTypical RepresentationExperiments with Magnets ShowCurrent Carrying WireSlide 28Compass and B FieldPlanet EarthInside it all.On the surface it looks like this..Inside: Warmer than FloriduhMuch Warmer than FloriduhFinallyIn BetweenSlide 37Our Earth has a magnetic field.RepeatA Look at the PhysicsNicer PictureAnother Picture The Vector Cross ProductPracticeUnitsteslas areThe Magnetic Force is Different From the Electric Force.Slide 47The Right Hand RuleThe effect of the sign of a movingMass SpectrometerSlide 51An ExampleProblem ContinuedSlide 54Slide 55PHY 2054 Magnetism - IPHY 2054 Magnetism - IAn Attractive New TopicAn Attractive New TopicThis Magnetic WeekThis Magnetic WeekToday we begin chapter 20 – MagnetismToday we begin chapter 20 – MagnetismThere will be NO CLASS on MONDAYThere will be NO CLASS on MONDAY•There will be a PowerPoint presentation posted. There will be a PowerPoint presentation posted. Run it as a presentation (click the screen icon Run it as a presentation (click the screen icon bottom right) and it will play as a recording. bottom right) and it will play as a recording. Print it as usual.Print it as usual.Wednesday – We will continue with Wednesday – We will continue with magnetism – assuming that you have magnetism – assuming that you have viewed the Monday Lecture.viewed the Monday Lecture.Quiz next FridayQuiz next FridayMagnetismMagnetism22WELCOME BACKWELCOME BACKEXAMS WILL EVENTUALLY BE RETURNED MaybeEXAMS WILL EVENTUALLY BE RETURNED MaybeMagnetismMagnetism33How Did You Do??How Did You Do??A. 80-100A. 80-100B. 60-79B. 60-79C. 40-59C. 40-59D. 20-39D. 20-39E. 0-19E. 0-19F. Less than 0F. Less than 0MagnetismMagnetism44Did the Card Help?Did the Card Help?A.A.A LotA LotB.B.A LittleA LittleC.C.Not reallyNot reallyD.D.NoNoMagnetismMagnetism55Magnetism was known Magnetism was known long ago.long ago.RefrigeratorMagneticsMagnetism 7Lodestone (Mineral)•Lodestones attracted iron filings.•Lodestones seemed to attract each other.•Lodestone is a natural magnet.Magnetism 8New ConceptThe Magnetic Field–We give it the symbol B.–A compass will line up with it.–It has Magnitude and direction so it is a VECTOR.•There are some similarities with the Electric Field but also some significant differences.Magnetism 9Magnetism•Refrigerators are attracted to magnets!Where is Magnetism Used??Where is Magnetism Used??•Motors•Navigation – Compass•Magnetic Tapes–Music, Data•Older Television Tubes & Oscilloscopes–Beam deflection Coil•Magnetic Resonance ImagingMagnetism 10And in magnets!!Although the magnet on the left is an electromagnet/huge and the one on the right is a permanent magnet/small, the idea is the same.Compare to ElectrostaticsMagnetism 12NSPivotMagnetWhat Happens??• Notice the general behavior trends of attraction and repulsion, dipole or monopole.Magnets•Like Poles Repel•Opposite Poles Attract•Magnetic Poles are only found in pairs.–No magnetic monopoles have ever been observed.Magnetism 14Shaded End is NORTH PoleShaded End of a compass pointsto the NORTH.S NObservations•Bring a magnet to an electrically charged object and the observed attraction will be a result of charge induction or polarization.•Magnetic poles do not interact with stationary electric charges.•Bring a magnet near some metals (Co, Fe, Ni …) and it will be attracted to the magnet.–The metal will be attracted to both the N and S poles independently.–Some metals are not attracted at all. (Al, Cu, Ag, Au)–Wood is NOT attracted to a magnet.–Neither is water.•A magnet will force a compass needle to align with it. (No big Surprise.)Magnetism 15MagnetsMagnetism 16Cutting a bar magnet in half produces TWO bar magnets, each with N and S poles.Magnetic FieldN S N SConsider a Permanent MagnetMagnetism 17N SBThe magnetic Field B goes from North to South.Introduce Another Permanent MagnetMagnetism 18N SBNSThe bar magnet (a magnetic dipole) wants to align with the B-field.pivotField of a Permanent MagnetMagnetism 19The south pole of the small bar magnet is attracted towards the north pole of the big magnet. The North pole of the small magnet is repelled by the north pole of the large magnet. The South pole of the large magnet creates a smaller force on the small magnet than does the North pole. DISTANCE effect.The field attracts and exerts a torque on the small magnet.N SBNSField of a Permanent MagnetMagnetism 20N SBN SThe bar magnet (a magnetic dipole) aligns with the B-field.It is now happy!Electric field of an electric dipoleMagnetism 21Electric FieldMagnetic FieldThe magnet behaves just like theElectric dipole and aligns itself withA MAGNETIC field.Similarities will continue.Iron filings will align as a compass does – • Each small filing lines up tangent to the field lines allowing a visual demonstrationExamples of Creating Magnetic fields• Fields are created by electric currents in a variety of ways and observed in a variety of places.Convention For Magnetic FieldsMagnetism 24 X Field INTO Paper Field OUT of Paper BTypical RepresentationMagnetism 25BB is a vector!Experiments with Magnets Show•Current carrying wire produces a circular magnetic field around it.•Force (actually torque) on a Compass Needle (or magnet) increases with current.Magnetism 26Current Carrying WireMagnetism 27Current intothe page.BRight hand Rule-Thumb in direction of the currentFingers curl in the direction of BCurrent Carrying WireCurrent Carrying Wire•B field is created at ALL POINTS in space surrounding the wire.•The B field has magnitude and direction.•Force on a magnet increases with the current.•Force is found to vary as ~(1/d) from the wire.Magnetism 28Compass and B Field•Observations–North Pole of magnets tend to move toward the direction of B while S pole goes the other way.–Field exerts a TORQUE on a