11/21/2011. The Magnetic Field. Chapter 24 Magnetic Fields and Forces. Mapping Out the Magnetic Field Using Iron Filings

Transcription

1 Chapter 24 Magnetic Fields and Forces Topics: 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 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 The Magnetic Field Slide 24-7 Mapping Out the Field of a Bar Magnet Mapping Out the Magnetic Field Using Iron Filings Slide 24-8 Slide 24-9 Drawing Field Lines of a Bar Magnet Magnetic Fields Produced by Bar Magnets Two bar magnets, unlike poles facing Two bar magnets, like poles facing Slide Slide

2 Checking Understanding Magnetic Fields Around Us Slide Slide Electric Currents Also Create Magnetic Fields The Magnetic Field of a Straight Current-Carrying Wire A long, straight wire A current loop A solenoid Slide Slide Representing Vectors and Currents That Are Perpendicular to the Page Slide Slide

3 Checking Understanding Point P is 5 cm above the wire as you look straight down at it. In which direction is the magnetic field at P? Answer Point P is 5 cm above the wire as you look straight down at it. In which direction is the magnetic field at P? Slide Slide Drawing Field Vectors and Field Lines of a Current-Carrying Wire Drawing a Current Loop Slide Slide The Magnetic Field of a Current Loop The Magnetic Field of a Solenoid A short solenoid A long solenoid Slide Slide

4 The Magnitude of the Field due to a Long, Straight, Current-Carrying Wire B = µ 0 I 2πr µ 0 = permeability constant = T m/a Checking Understanding The magnetic field at point P is zero. What are the magnitude and direction of the current in the lower wire? A. 10 A to the right. B. 5 A to the right. C. 2.5 A to the right. D. 10 A to the left. E. 5 A to the left. F. 2.5 A to the left. Slide Slide Answer The magnetic field at point P is zero. What are the magnitude and direction of the current in the lower wire? The Magnetic Field of a Current Loop B = µ 0 I 2R Magnetic field at the center of a current loop of radius R E. 5 A to the left. B = µ 0 NI 2R Magnetic field at the center of a current loop with N turns Slide Slide Example The Magnetic Field Inside a Solenoid What is the direction and magnitude of the magnetic field at point P, at the center of the loop? B = µ 0 I N L Magnetic field inside a solenoid of length L with N turns. Slide Slide

5 The Force on a Charged Particle Moving in a Magnetic Field The Right-Hand Rule for Forces Slide Slide Paths of Charged Particles in Magnetic Fields The Mass Spectrometer r = mv qb Slide Slide Magnetic Fields Exert Forces on Currents Forces between Currents Magnetic force between two parallel current-carrying wires F parallel wires = µ 0 LI 1 I 2 2πd F wire = ILB Magnitude of the force on a current segment of length L perpendicular to a magnetic field Slide Slide

6 11/21/2011 A Current Loop Acts like a Bar Magnet Magnetic Fields Exert Torques on Current Loops Slide Magnetic Resonance Imaging Slide Magnetic Resonance Imaging Slide Slide The Electric Motor Slide