Chapter 19 MagnetismSlide 2Slide 3Slide 4Slide 5Slide 6Slide 7Nature of MagnetismMagnetic ForceMagnetism and ElectricityEarth’s Magnetic FieldSlide 12A Moving Charge in Magnetic FieldRight Hand RuleSlide 15A charged particle moves in a straight line through a certain region of space. The magnetic field in that region (a) has a magnitude of zero, (b) has a zero component perpendicular to the particle's velocity, or (c) has a zero component parallel to the particle's velocity.(b). The force that a magnetic field exerts on a charged particle moving through it is given by F = qvB sin θ = qvB , where B is the component of the field perpendicular to the particle’s velocity. Since the particle moves in a straight line, the magnetic force (and hence B , since qv ≠ 0) must be zero.The north-pole end of a bar magnet is held near a stationary positively charged piece of plastic. Is the plastic (a) attracted, (b) repelled, or (c) unaffected by the magnet?(c). The magnetic force exerted by a magnetic field on a charge is proportional to the charge’s velocity relative to the field. If the charge is stationary, as in this situation, there is no magnetic force.Slide 20Slide 21Slide 22As a charged particle moves freely in a circular path in the presence of a constant magnetic field applied perpendicular to the particle's velocity, its kinetic energy (a) remains constant, (b) increases, or (c) decreases.(a). The magnetic force acting on the particle is always perpendicular to the velocity of the particle, and hence to the displacement the particle is undergoing. Under these conditions, the force does no work on the particle and the particle’s kinetic energy remains constant.Two charged particles are projected into a region in which a magnetic field is perpendicular to their velocities. After they enter the magnetic field, you can conclude that (a) the charges are deflected in opposite directions, (b) the charges continue to move in a straight line, (c) the charges move in circular paths, or (d) the charges move in circular paths but in opposite directions.(c). Anytime the velocity of a charged particle is perpendicular to the magnetic field, it will follow a circular path. The two particles will move in opposite directions around their circular paths if their charges have opposite signs, but their charges are unknown so (d) is not an acceptable answer.Slide 27Slide 28Slide 29Slide 30An Electric Current in a Magnetic FieldSlide 32Chapter 19 MagnetismChapter 19 MagnetismMagnetic FieldElectric Current and Magnetic fieldForce on an Electric Current in a Magnetic FieldForce on an Moving Electric Charge in a Magnetic FieldMaglev TrainMaglev TrainMore than 30 magnets in a carMore than 30 magnets in a carMagnetic ResonanceMagnetic Resonance Imaging (MRI)Imaging (MRI)Magnetic Resonance Imaging (MRI)An imaging technique used primarily in medical settings to produce high quality images of the inside of the human body MRI is based on the principles of nuclear magnetic resonance (NMR) The human body is primarily fat and waterThe human body is primarily fat and water. . Fat and water have many hydrogen atoms which makeFat and water have many hydrogen atoms which make the human body approximately 63% hydrogen atoms. Hydrogen nuclei have an NMR signal.the human body approximately 63% hydrogen atoms. Hydrogen nuclei have an NMR signal. For these reasons magnetic resonance imaging primarily images the NMR signal from the hydrogen nuclei.For these reasons magnetic resonance imaging primarily images the NMR signal from the hydrogen nuclei.National High Magnetic Field LaboratoryNational High Magnetic Field Laboratory Tallahassee, FloridaNMR FacilityDC MagnetsCondensed Matter GroupsOfficesHybrid Magnet 45 TmK Lab (20 T)1.43GWGenerator(600MW, 600MJ)60T controlledPulse Magnet, 32 mm liq. N bore45 T hybrid, 32 mm bore12 T, 40 cm warm bore MRI magnet (Magnex)High B/T FacilityOperated by:• Florida State University• University of Florida• Los Alamos National Lab Supported by:• National Science Foundation• State of FloridaNature of MagnetismNature of Magnetism2 1+Q+QF12F21r12I IF FIIF FMagnetic ForceMagnetic Force The forces that come into being when electric currents interact are called magnetic forcesmagnetic forces, or magnetic forces magnetic forces arise from the interactions of moving chargesarise from the interactions of moving charges. (The electrical force is between two charges at restat rest) There is only a single interaction between charges, electromagnetic interaction. It is always possible to separate the force on a charge into an electric part, which is independent of its motion, and a magnetic part, which is proportional to its speed relative to the observer.Magnetism and ElectricityMagnetism and Electricity A electric current produces a magnetic field A magnet moving near a wire produces electricityIt is impossible to have one without the otherEarth’s Magnetic Field•The Earth’s magnetic field resembles that achieved by burying a huge bar magnet deep in the Earth’s interiorThe combination of heat and the Earth’s rotation makes the molten outer core swirl around, creating massive electrical currentsmassive electrical currents that generates the magnetic fieldthat generates the magnetic field by the electromagnetic effect Molten outer core Solid inner coreA Moving Charge in Magnetic Field Magnetic field, B, is defined in terms of the magnetic force F on a moving charge:Magnetic field magnitude: B=F/QB=F/QvvsinsinororF=BQvsin(electric field: E=F/Q)No force acts on a charge moving in the direction of B (Q=0)FFmaxmax=BQv if =BQv if =90=90oo or sin or sin=1=1Direction of B: Right-hand rule vFBQUnit: 1 tesla=1 T=1 N/A·m (1T=104 gauss (G))The magnitude of the earth’s B is 3x10-5 TEngineer Nikola Tesla (1856-1943)Right Hand Rule•Hold your right hand open•Place your fingers in the direction of B•Place your thumb in the direction of v•The direction of the force on a positive charge is directed out of your palm–If the charge is negative, the force is opposite that determined by the right hand rule.v-eBFFv-eBQUICK QUIZ 19.1A charged particle moves in a straight line through a certain region of space. The magnetic field in that region (a) has a magnitude of zero, (b) has a zero component perpendicular to the particle's velocity, or (c) has a zero component parallel to the particle's velocity.QUICK QUIZ 19.1 ANSWER(b). The