Copyright © 2007 Pearson Education, Inc. publishing as Addison-Wesley Goals for Chapter 20 To observe and visualize magnetic fields and forces. To study the motion of a charged particle in a magnetic field. To evaluate the magnetic force on a current-carrying conductor. To determine the force and torque produced with a magnet and current-carrying loop of wire (the DC motor). To study the fields generated by long, straight conductors. To observe the changes in the field with the conductor in loops (forming the solenoid). To calculate the magnetic field at selected points in space. To understand magnetism via magnetic moments.

Copyright © 2007 Pearson Education, Inc. publishing as Addison-Wesley The behavior of bar magnets – Figures 20.2,20.3 Notice the general behavior trends of attraction and repulsion, dipole or monopole.

Copyright © 2007 Pearson Education, Inc. publishing as Addison-Wesley Our Earth itself has a magnetic field. – Figure 20.4 This field is not very strong but it is consistent (and convenient) as the next slide will show.

Copyright © 2007 Pearson Education, Inc. publishing as Addison-Wesley A compass will align with fields – Figure 20.5 The compass will align with whatever average field is strongest. In figure 20.5, the field caused by the current in the wire is stronger than that any background field from the earth. Absent the current-carrying wire, the compass would align with the earth’s magnetic field. This allows a consistent direction to be determined by someone with the need for navigation.

Copyright © 2007 Pearson Education, Inc. publishing as Addison-Wesley Examples of Magnetic Fields – Figure 20.7 Fields are created in a variety of ways and observed in a variety of places.

Copyright © 2007 Pearson Education, Inc. publishing as Addison-Wesley Iron filings will align as a compass does – Figure 20.8 Each small filing lines up tangent to the field lines allowing a visual demonstration

Copyright © 2007 Pearson Education, Inc. publishing as Addison-Wesley The equipotential map around charges – Figure Around an charge or arrangement of charges regions of equal potential may be drawn as equal-potential lines.

Copyright © 2007 Pearson Education, Inc. publishing as Addison-Wesley Charges moving with respect to a field – Figure 20.9 The effect of an existing magnetic field on a charge depends on the charges direction of motion relative to the field.

Copyright © 2007 Pearson Education, Inc. publishing as Addison-Wesley The Right Hand Rule – Figure Using the right hand rule, one may determine the direction of the field produced by a moving positive charge.

Copyright © 2007 Pearson Education, Inc. publishing as Addison-Wesley The effect of the sign of a moving charge – Figure Positive and negative charges will feel opposite effects from a magnetic field.

Copyright © 2007 Pearson Education, Inc. publishing as Addison-Wesley Magnetic force may be calculated – Figure Refer to the Conceptual Analysis, the Problem-Solving Strategy, and Example 20.1 on pages 664 and 665 of your text.

Copyright © 2007 Pearson Education, Inc. publishing as Addison-Wesley Magnetic fields will alter ionic movement – Figure You can create electrostatic lenses that will focus or alter the path or velocity of ions or electrons. This is the foundation of modern mass spectroscopy. Refer to the Conceptual Analysis on page 666 and Example 20.3 on page 670.

Copyright © 2007 Pearson Education, Inc. publishing as Addison-Wesley The Magnetron operating in your home – Figure A serendipitous discovery of radar research, the microwave oven uses a magnetron to trap electronic oscillations with wavelengths between.001 and 10m. Refer to Conceptual Analysis 20.3 on page 668 of your text.

Copyright © 2007 Pearson Education, Inc. publishing as Addison-Wesley Introduction of helical motion – Figure Such motion can be imparted to ions given velocities both parallel and perpendicular to the applied field. Refer to Conceptual Analysis 20.4 and Example 20.2 in your text.

Copyright © 2007 Pearson Education, Inc. publishing as Addison-Wesley Force on a conductor with current – Figures 20.22, 23 When a conductor, often a wire, carrying current is exposed to an external magnetic field, a force is exerted on the conductor.

Copyright © 2007 Pearson Education, Inc. publishing as Addison-Wesley Applications of force on a conductor – Figures 20.25,26 Novel applications have been devised to make use of the force that a magnetic field exerts on a conductor carrying current. Refer to Conceptual Analysis 20.5 and Example 20.4 in your text.

Copyright © 2007 Pearson Education, Inc. publishing as Addison-Wesley The motor – Figure If the conductor is a loop, the torque can create an electric motor.

Copyright © 2007 Pearson Education, Inc. publishing as Addison-Wesley Magnetic field of long straight conductor – Figure 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. Refer to Conceptual Analysis 20.7 and Example 20.6

Copyright © 2007 Pearson Education, Inc. publishing as Addison-Wesley Fields in two conductors side-by-side – Figure This was the classic demonstration done by Ampere as he demonstrated the effect. Refer to Example 20.7.

Copyright © 2007 Pearson Education, Inc. publishing as Addison-Wesley Currents in a loop – Figures 20.39, 40 This will allow us to generate a field inside loops of conductor carrying current. Refer to Example 20.8.

Copyright © 2007 Pearson Education, Inc. publishing as Addison-Wesley Magnetic field of long straight conductor – Figure 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. Refer to Conceptual Analysis 20.7 and Example 20.6

Copyright © 2007 Pearson Education, Inc. publishing as Addison-Wesley The solenoid – Figure Generating a field inside a cylinder which already contains a permanent magnet will cause a force and move the permanent magnet. Refer to Conceptual Analysis 20.8.