Magnetism – Part II (Chapter 20 20.2 – Start of 20.5)NOTE You may have to click to next slideThis weekA Look at the PhysicsNicer PictureAnother Approach The Vector Cross ProductPracticeUnitsteslas areThe Magnetic Force is Different From the Electric Force.Slide 11The Right Hand RuleSome important applicationsThe Velocity SelectorSlide 15Charge moving perpendicular to magnetic fieldLook at the direction of the force and the velocitySlide 18Slide 19Slide 20Slide 21Off AngleThe Mass SpectrometerMass SpectrometerSlide 25Secondary Ion Mass SpectrometerSlide 27Slide 28Forces on Current Carrying ConductorsThe Force on a Current Carrying ConductorSlide 31Enough for one Session?This is a recorded lecture and it covers forces generated by magnetic fields on moving charges, including currents. I have not done this before so it may seem a bit amateurish. Please start this as a presentation by clicking on the “screen” button at the lower right at the bottom of this PowerPoint window. You can also treat it as a normal slide presentation for printing, etc. This material will NOT be covered in our regular class, so consider this a replacement for the lecture session. SEND ME AN EMAIL IF YOU EXPERIENCE ANY PROBLEMS WITH THIS. Use “PROBLEMS” as the subject.NOTEYOU MAY HAVE TO CLICK TO NEXT SLIDEMagnetism 2NO CLASS on MondayThere will be a problem session Wednesday morning at 7:00 AM mostly treating problems related to this lecture.There will be a QUIZ on Friday on Magnetism. It includes the material in this presentation.Normal classes on Wednesday & Friday.I am sorry that I wasn’t able to be in class on Monday. Perhaps you will like this format better … you can turn me off whenever you like!Magnetism3A Look at the PhysicsMagnetism 4BqThere is NO force ona charge placed into amagnetic field if thecharge is NOT moving.Bqv• If the charge is moving in a different direction, thereis a force on the charge,perpendicular to both v and B. F = q v BThere is no force if the chargemoves parallel to the field.Nicer PictureMagnetism 5Rotate v into B using the right hand rule!Another ApproachThe Vector Cross ProductMagnetism 6)sin(qvBFq BvF(Not Required)PracticeMagnetism 7Which way is the Force???UnitsMagnetism 8 m)-N/(A 1 T 1 tesla1 mAmpN/:)sCmNqvFBUnitsBqv Sin(θFteslas areMagnetism 9The Magnetic Force is Different From the Electric Force.Whereas the electric force acts in the same direction as the field:The magnetic force acts in a direction orthogonal to the field: And --- the charge must be moving !!)sin(qvBF F qE(Use “Right-Hand” Rule to determine direction of F)• The effect of an existing magnetic field on a charge depends on the charges direction of motion relative to the field.The Right Hand RuleSOME IMPORTANT APPLICATIONSVelocity selector deviceMass SpectrometerCyclotronMagnetism13The Velocity SelectorMagnetism 14EvX BFEFBMagnetism15What is the relation between the intensities of the electric and magnetic fields for the particle to move in a straight line ?.•FEFBFE = q E and FB = q v BIf FE = FB the particle will movefollowing a straight line trajectoryq E = q v Bv = E / Bxxxxxx•q mBvEBECHARGE MOVING PERPENDICULAR TO MAGNETIC FIELDLOOK AT THE DIRECTION OF THE FORCE AND THE VELOCITYMagnetism17Magnetism18frequencyangular cyclotron thecalled is Thisv/ror r v:Recallrmv qvBqvB is force magnetic Thermv Force lCentripetarv on Accelerati lCentripetaRECALL222mBqrvBqmvrIMPORTANT does not depend on rMagnetism19BqmvrmBqfperiodTf12Magnetism20CYCLOTRONMagnetism21Synchrotrons are HUGE!!OFF ANGLEMagnetism22THE MASS SPECTROMETERMASS SPECTROMETERConsider any mixed material that is a gas or can be converted to a gas (high temperature).Suppose you want to know what the mixture contains.Urine analysis for drugs.Analysis of minerals for small quantities of impurities. Analysis of semiconductor materialsMagnetism24“Sputtering”To Mass SpectrometerMass SpectrometerMagnetism 25Smaller MassSecondary Ion Mass SpectrometerMagnetism 26MagnetIon SourceSample LocationIn this case, thestrength of the magnetis increased with timeso that each masspasses over a “slit”in front of the iondetectorDetectorMagnetism 27SLITMagnetic Sector Mass SpectrometerMagnetism 28Trace of Volatile Organics Compounds in AirMagnetism29IThe Force on a Current Carrying Conductor•Consider the diagram shown on the left.•Assume that in time “t”, a number of charge q flow through the wire.•The force on this charge is Bqv (I left off the subscript d for the drift.)•This force acts on all of the charges in the volume of length l and area A.•Suppose there are “N” of these per unit volume. Then the TOTAL number of charges is NlA. (Number per unit volume x length x Area. (lA=volume)Magnetism 30IMagnetism 31•Consider the diagram shown on the left.•Assume that in time “t”, a number of charge q flow through the length l of the wire.•The force on each charge is Bqv (I left off the subscript d for the drift.)•This force acts on all of the charges in the volume of length l and area A.•Suppose there are “N” of these per unit volume. Then the TOTAL number of charges is NlA. (Number per unit volume x length x Area. (lA=volume)BIlFtqNlAINlAtlNAqBlNAqvBlFtlvNAqvBlBqvNlAF/charges#)()(/)(IEnough for one Session?•A Yes•B Yes•C Yes•D Yes•E
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