1. Admin: mid-term 2 grades and solutions posted. Scripts back at the end Average = 84% (up from 72%). Excellent work! Assignment 10 posted. Due on Monday (May 18 th ) Missed assignments can be completed up until the final (May 22 nd ). The class is over after the final exam no extensions or late assignments after this. Any issues with grades (labs, assignments, mid-terms) must be resolved before then with me or your TA.

2. F0 D-59.5 D62.5 D+66.5 C-69.5 C72.5 C+76.5 B-79.5 B82.5 B+86.5 A-89.5 A92.5 72%84%75%89%93% 10.8212.5622.5017.7018.5582.13 Mt1 (15%) Mt2 (15%) Final (30%) MastPhys (20%) Labs (20%) Average Points Grading scheme (and how to calculate your grade)

3. Copyright © 2009 Pearson Education, Inc. Chapter 27 Magnetism

4. Copyright © 2009 Pearson Education, Inc. A uniform magnetic field is constant in magnitude and direction. The field between these two wide poles is nearly uniform. 27-1 Magnets and Magnetic Fields

5. Copyright © 2009 Pearson Education, Inc. Experiment shows that an electric current produces a magnetic field. The direction of the field is given by a right-hand rule. 27-2 Electric Currents Produce Magnetic Fields

6. Copyright © 2009 Pearson Education, Inc. 27-2 Electric Currents Produce Magnetic Fields Here we see the field due to a current loop; the direction is again given by a right-hand rule.

7. Copyright © 2009 Pearson Education, Inc. A magnet exerts a force on a current- carrying wire. The direction of the force is given by a right- hand rule. 27-3 Force on an Electric Current in a Magnetic Field; Definition of B

8. Copyright © 2009 Pearson Education, Inc. Internet hints…

9. Copyright © 2009 Pearson Education, Inc. The force on the wire depends on the current, the length of the wire, the magnetic field, and its orientation: This equation defines the magnetic field B. In vector notation : 27-3 Force on an Electric Current in a Magnetic Field; Definition of B

10. Copyright © 2009 Pearson Education, Inc. Vector Cross Product; The vector cross product is defined as: The direction of the cross product is defined by a right-hand rule: http://www.mrbigler.com/moodle/mod/resource/view.php?id=3721

11. Copyright © 2009 Pearson Education, Inc. Vector Cross Product; The cross product can also be written in determinant form:

12. Copyright © 2009 Pearson Education, Inc. 11-2 Vector Cross Product; Torque as a Vector Some properties of the cross product:

13. Copyright © 2009 Pearson Education, Inc. Unit of B : the tesla, T: 1 T = 1 N/A·m. Another unit sometimes used: the gauss ( G ): 1 G = 10 -4 T. 27-3 Force on an Electric Current in a Magnetic Field; Definition of B

14. Copyright © 2009 Pearson Education, Inc. Just for interest…

15. Copyright © 2009 Pearson Education, Inc. 27-3 Force on an Electric Current in a Magnetic Field; Definition of B Example 27-1: Magnetic Force on a current-carrying wire. A wire carrying a 30-A current has a length l = 12 cm between the pole faces of a magnet at an angle θ = 60°, as shown. The magnetic field is uniform at 0.90 T. What is the magnitude of the force on the wire?

16. Copyright © 2009 Pearson Education, Inc. 27-3 Force on an Electric Current in a Magnetic Field; Definition of B Example 27-2: Measuring a magnetic field. A rectangular loop of wire hangs vertically as shown. A magnetic field B is directed horizontally, perpendicular to the wire, and points out of the page at all points. The magnetic field is very nearly uniform along the horizontal portion of wire ab (length l = 10.0 cm) which is near the center of the gap of a large magnet producing the field. The top portion of the wire loop is free of the field. The loop hangs from a balance which measures a downward magnetic force (in addition to the gravitational force) of F = 3.48 x 10 -2 N when the wire carries a current I = 0.245 A. What is the magnitude of the magnetic field B?

17. Copyright © 2009 Pearson Education, Inc. Example 27-3: Magnetic Force on a semicircular wire. A rigid wire, carrying a current I, consists of a semicircle of radius R and two straight portions as shown. The wire lies in a plane perpendicular to a uniform magnetic field B 0. Note choice of x and y axis. The straight portions each have length l within the field. Determine the net force on the wire due to the magnetic field B 0. See the book for the full solution (there are some tricks)