Magnetism – Part 3CalendarAbout those exams -These were the hints I gave you!Slide 5Slide 6Look at the direction of the force and the velocitySlide 8Slide 9Off AnglePROBLEMForce on a Wire Carrying a Current in a B FieldSlide 13Slide 14Current LoopThe Loop (From the top)The other sidesApplication: The motorSlide 19Slide 20Slide 21Slide 22Another Application The GalvanometerCurrents Cause Magnetic FieldsMagnetic field of long straight conductor –ResultForce Between Two Current Carrying ConductorsTwo WiresCurrents in a loop –Field of a Current LoopSlide 31SolonoidThe solenoid –Slide 34MAGNETISM – PART 3CALENDARMonday – Recorded Lecture.Today – Brief review of the material + a few problems.Today, Friday we will continue with chapter 20 materials.There will be a Quiz on Magnetism on Friday.2MagnetismABOUT THOSE EXAMS -Grades look pretty bad. I will review on Friday after I have a look at the papers.Each exam (both sections) had similar problems.A Kirchoff Law Problem – simpleA combine either capacitors or resistors and calculate what was happening at one of them.A problem involving polarization – a thinker.A question on how much energy was required to bring three charges together.3MagnetismTHESE WERE THE HINTS I GAVE YOU!Anything in the three chapters is fair game.Read the sections on charge and charge effects very carefully. We didn’t cover some of this in class. (Problem 2)Know the difference between Potential and Potential energy.Know how much work it takes to create a charge distribution. We did it in class. (Problem 1)Know how to add capacitors and resistors and how to solve simple circuit problems. (Problem 3)There WILL be a Kirchhoff's Law problem. (Problem 4)Coulomb’s Law and the addition of forces. Calculation of the potential (scalar)Be sure to understand all of the HW problems that were assigned – or not assigned!4Magnetism5The force is perpendicularto the direction of motion.The force has a constant magnitude = BqvThis will produce circularmotion as in PHY2053.Magnetism6MagnetismLOOK AT THE DIRECTION OF THE FORCE AND THE VELOCITYMagnetism7Magnetism8frequencyangular cyclotron thecalled is Thisv/ror r v:Recallrmv qvBqvB is force magnetic Thermv Force lCentripetarv on Accelerati lCentripetaRECALL222mBqrvBqmvrMagnetism9BqmvrmBqfperiodTf12OFF ANGLEMagnetism10TvPPITCHparallelPPROBLEM11An electron at point A in the figure has a speed v0 of 1.4 x 106 m/s. Find (a)the magnitude and direction of the magnetic field that will cause the electron to follow the semicircular path from A to B and (b) the time required for the electron to move from A to B. (c)What magnetic field would be needed if the particle were a proton instead of an electron?m=9.1E-31 Kge=1.6E-19 CMagnetismFORCE ON A WIRE CARRYING A CURRENT IN A B FIELDBilF 13A straight vertical wire carries a current of 1.20 A downward in a region between the poles of a large electromagnet where the field strength is 0.588 T and is horizontal. What are the magnitude and direction of the magnetic force on a 1.00 cm section of this wire if the magnetic-field direction is (a)toward the east, (b) toward the southMagnetism• Novel applications have been devised to make use of the force that a magnetic field exerts on a conductor carrying current.Magnetism14Magnetism15CURRENT LOOPLoop will tend to rotate due to the torque the field applies to the loop.What is forceon the ends??Magnetism16THE LOOP (FROM THE TOP)pivotOBSERVATIONForce on Side 2 is outof the paper and that onthe opposite side is into the paper. No net forcetending to rotate the loopdue to either of these forces.The net force on the loop is also zero,Magnetism17THE OTHER SIDES1=F1 (b/2)Sin() =(B i a) x (b/2)Sin()total torque on the loop is: 21Total torque:=(iaB) bSin() =iABSin()(A=Area)APPLICATION: THE MOTOR If the conductor is a loop, the torque can create an electric motor.Magnetism19Magnetism20Magnetism2122A circular coil of wire 8.6 cm in diameter has 15 turns and carries a current of 2.7 A. The coil is in a region where the magnetic field is 0.56 T. What orientation of the coil gives the maximum torque on the coil.What is this maximum torque? MagnetismMagnetism23ANOTHER APPLICATIONTHE GALVANOMETERCURRENTS CAUSE MAGNETIC FIELDSMagnetism24MAGNETIC FIELD OF LONG STRAIGHT CONDUCTOR – • Placed over a compass, the wire would cause the compass needle to deflect. This was the classic demonstration done by Oersted as he demonstrated the effect.Magnetism25RESULTMagnetism26r(exact) 1042700ATmrIBMagnetism27FORCE BETWEEN TWO CURRENT CARRYING CONDUCTORSFirst wire produces a magnetic field at the second wire position.The second wire therefore feels a force = BilTWO WIRESMagnetism28rIIlFlIrIlBIFrI222BFirst Wire From B210210210CURRENTS IN A LOOP – Magnetism29FIELD OF A CURRENT LOOPMagnetism30RNIB20N turns of wireMagnetism31SOLONOIDMagnetism32LengthTurns ofnumber Total0LNnnIBB=~0 outsideTHE SOLENOID – Magnetism33rNIB20B=0
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