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Slide 1Lightning Review19.10 Magnetic Field of a current loop19.11 Magnetic Field of a solenoidSolenoid MagnetSlide 6Example: Magnetic Field inside a Solenoid.Slide 8Chapter 20 Induced EMF and InductionIntroduction20.1 Induced EMF and magnetic fluxProblem: determining a fluxSlide 13Slide 1420.2 Faraday’s law of inductionSlide 16Does there have to be motion?Slide 18Slide 19Slide 20Maybe the B-field needs to change…..Slide 22Slide 23Faraday’s law of magnetic inductionApplications:Example : EMF in a loopSlide 271101/14/1901/14/19General Physics (PHY 2140)Lecture 15Lecture 15 Electricity and MagnetismMagnetism Applications of magnetic forces Induced voltages and induction Magnetic flux and induced emf Faraday’s lawChapter 19-20http://www.physics.wayne.edu/~apetrov/PHY2140/2201/14/1901/14/19Lightning ReviewLightning ReviewLast lecture: 1.1.MagnetismMagnetismCharged particle in a magnetic fieldCharged particle in a magnetic fieldAmpere’s law and applicationsAmpere’s law and applicationsReview Problem: A rectangular loop is placed in a uniform magnetic field with the plane of the loop parallel to the direction of the field. If a current is made to flow through the loop in the sense shown by the arrows, the field exerts on the loop:1. a net force.2. a net torque.3. a net force and a net torque.4. neither a net force nor a net torque.mvrqB=sinF BIl q=sinNBIAt q=02IBrmp=3301/14/1901/14/1919.10 Magnetic Field of a current loop19.10 Magnetic Field of a current loopMagnetic field produced by a wire can be enhanced Magnetic field produced by a wire can be enhanced by having the wire in a loop.by having the wire in a loop.x1Ix2B4401/14/1901/14/1919.11 Magnetic Field of a solenoid19.11 Magnetic Field of a solenoidSolenoid magnet consists of a wire coil with multiple Solenoid magnet consists of a wire coil with multiple loops.loops.It is often called an electromagnet.It is often called an electromagnet.5501/14/1901/14/19Solenoid MagnetSolenoid MagnetField lines inside a solenoid magnet are parallel, uniformly spaced Field lines inside a solenoid magnet are parallel, uniformly spaced and close together.and close together.The field inside is uniform and strong.The field inside is uniform and strong.The field outside is non uniform and much weaker.The field outside is non uniform and much weaker.One end of the solenoid acts as a north pole, the other as a south One end of the solenoid acts as a north pole, the other as a south pole.pole.For a long and tightly looped solenoid, the field inside has a value:For a long and tightly looped solenoid, the field inside has a value:oB nIm=6601/14/1901/14/19Solenoid MagnetSolenoid Magnetn = N/ln = N/l : number of (loop) turns per unit length. : number of (loop) turns per unit length.I I : current in the solenoid. : current in the solenoid.oB nIm=74 10 /oTm Am p-= �7701/14/1901/14/19Example: Magnetic Field inside a Solenoid.Example: Magnetic Field inside a Solenoid.Consider a solenoid consisting of 100 turns of wire and Consider a solenoid consisting of 100 turns of wire and length of 10.0 cm. Find the magnetic field inside when it length of 10.0 cm. Find the magnetic field inside when it carries a current of 0.500 A.carries a current of 0.500 A.N = 100l = 0.100 mI = 0.500 A( )( ) ( )741001000 /0.104 10 / 1000 / 0.5006.28 10oN turnsn turns ml mB nI Tm A turns m AB Tm p--= = == = �= �74 10 /oTm Am p-= �8801/14/1901/14/19Comparison:Electric Field vs. Magnetic Field Electric MagneticSource Charges Moving ChargesActs on Charges Moving ChargesForce F = Eq F = q v B sin()Direction Parallel E Perpendicular to v,BField LinesOpposites Charges Attract Currents Repel9901/14/1901/14/19Chapter 20Chapter 20Induced EMF and InductionInduced EMF and Induction101001/14/1901/14/19IntroductionIntroductionPrevious chapter: electric currents produce magnetic Previous chapter: electric currents produce magnetic fields (Oersted’s experiments)fields (Oersted’s experiments)Is the opposite true: can magnetic fields create electric Is the opposite true: can magnetic fields create electric currents?currents?111101/14/1901/14/1920.1 Induced EMF and magnetic flux20.1 Induced EMF and magnetic fluxJust like in the case of electric flux, Just like in the case of electric flux, consider a situation where the magnetic consider a situation where the magnetic field is uniform in magnitude and field is uniform in magnitude and direction. Place a loop in the B-field.direction. Place a loop in the B-field.The flux, The flux, , is defined as the product of , is defined as the product of the field magnitude by the area crossed the field magnitude by the area crossed by the field lines.by the field lines.where is the component of B where is the component of B perpendicular to the loop, perpendicular to the loop,  is the angle is the angle between B and the normal to the loop.between B and the normal to the loop.Units: TUnits: T··mm22 or Webers (Wb) or Webers (Wb)cosB A BA q^F = =Definition of Magnetic FluxB^The value of magnetic flux is proportional to the total number of magnetic field lines passing through the loop.121201/14/1901/14/19A square loop 2.00m on a side is placed in a magnetic field of A square loop 2.00m on a side is placed in a magnetic field of strength 0.300T. If the field makes an angle of 50.0° with the strength 0.300T. If the field makes an angle of 50.0° with the normal to the plane of the loop, determine the magnetic flux normal to the plane of the loop, determine the magnetic flux through the loop. through the loop. Problem: determining a fluxProblem: determining a flux131301/14/1901/14/19A square loop 2.00m on a side is placed in a magnetic field of strength 0.300T. If the field makes an angle of 50.0° with the normal to the plane of the loop, determine the magnetic flux through the loop. Given:L = 2.00 mB = 0.300 T = 50.0˚ Find:=?Solution:From what we are given, we use cosBA qF =( ) ( )220.300 2.00 cos50.00.386T mTm==o141401/14/1901/14/1920.1 Induced EMF and magnetic flux20.1 Induced EMF and magnetic fluxTwo circuits are not connected: Two circuits are not connected: no current?no current?However, However, closing the switchclosing the switch we we see that the compass’ needle see that the compass’ needle movesmoves and then goes back to and then goes back to its previous positionits previous positionNothing happensNothing happens when the when the


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