Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Magnets and the magnetic field Electric currents create magnetic fields Magnetic fields of wires, loops, and solenoids Magnetic forces on charges and currents Magnets and magnetic materials Chapter 24 Magnetic Fields and Forces Topics: Sample question: This image of a patient’s knee was made with magnetic fields, not x rays. How can we use magnetic fields to visualize the inside of the body? Slide 24-1

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Electric Currents Also Create Magnetic Fields A long, straight wire A current loopA solenoid Slide 24-15

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. The Magnitude of the Field due to a Long, Straight, Current-Carrying Wire Slide Also μ 0 = 4π x T m / A

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. The Magnetic Field of a Current Loop Magnetic field at the center of a current loop of radius R Magnetic field at the center of a current loop with N turns Slide 24-29

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. The Magnetic Field Inside a Solenoid Magnetic field inside a solenoid of length L with N turns. Slide 24-31

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Right Hand Rules for Magnetism Right-hand rule 1 (RHR 1) => for finding magnetic force F B = q*v_vector x B_vector (Cross-Product Rule) 1.Point right hand in the direction the charges are moving (current or velocity) 2.Rotate your right hand until you can point your fingers in the direction of the magnetic Field 3.Thumb points in direction of force for + charge Force is in opposite direction for - charges Right-hand rule 2 (RHR 2) => Finding direction of B from I Point thumb of right hand in direction of current I, B-field lines curl in direction of fingers Right-hand rule 3 (RHR 3) => Finding direction of current in a loop from direction of B-field Point thumb of right hand in direction of B-field Fingers of right hand curl in direction of current Slide 24-2

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Magnetic Field Activities Slide Double Trouble Solenoid Questions from E4 Worksheet 1

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Magnetic Force Slide Review Magnetic Forces Magnetic Force on Moving Charges E4 Worksheet 2 Questions Torque on Current Loops Double Trouble with Current Loops

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Paths of Charged Particles in Magnetic Fields Slide 24-35

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. The Mass Spectrometer Slide 24-36

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Velocity Selector Slide 24-37

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Magnetic Fields Exert Forces on Currents Magnitude of the force on a current segment of length L perpendicular to a magnetic field Slide 24-37

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Forces between Currents Slide Magnetic force between two parallel current-carrying wires

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Slide 24-39

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Forces between Current Loops Slide 24-40

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. A Current Loop Acts like a Bar Magnet Slide 24-41

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Magnetic Fields Exert Torques on Current Loops Slide 24-42

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Applications: Galvanometers, Motors, Loudspeakers An electric motor also takes advantage of the torque on a current loop, to change electrical energy to mechanical energy.

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. The Torque on a Dipole in a Magnetic Field Slide 24-43

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Magnetic Resonance Imaging Slide 24-44

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Magnetic Resonance Imaging Slide 24-45

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Electron Magnetic Moments: Ferromagnetism A nonmagnetic solid (copper)A ferromagnetic solid (iron) Slide 24-47

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Inducing a Magnetic Moment in a Piece of Iron Slide 24-48

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Summary of Chapter 20 Magnets have north and south poles Like poles repel, unlike attract Unit of magnetic field: tesla Electric currents produce magnetic fields A magnetic field exerts a force on an electric current:

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Summary of Chapter 20 A magnetic field exerts a force on a moving charge: Magnitude of the field of a long, straight current-carrying wire: Parallel currents attract; antiparallel currents repel

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Summary of Chapter 20 Magnetic field inside a solenoid: Ampère’s law: Torque on a current loop:

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Checking Understanding The diagram below shows slices through two adjacent current loops. Think about the force exerted on the loop on the right due to the loop on the left. The force on the right loop is directed A.to the left. B.up. C.to the right. D.down. Slide 24-37

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Answer The diagram below shows slices through two adjacent current loops. Think about the force exerted on the loop on the right due to the loop on the left. The force on the right loop is directed A.to the left. B.up. C.to the right. D.down. Slide 24-38

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Additional Questions 1.A loop carrying a current as shown rests in a uniform magnetic field directed to the right. If the loop is free to rotate, A.it will rotate clockwise. B.it will not rotate. C.it will rotate counterclockwise. Slide 24-66

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Answer 1.A loop carrying a current as shown rests in a uniform magnetic field directed to the right. If the loop is free to rotate, A.it will rotate clockwise. B.it will not rotate. C.it will rotate counterclockwise. Slide 24-67

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Motional emf Slide 25-12

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Induced Current in a Circuit Slide 25-13

Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Magnetic Flux Slide 25-14