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adapted from http://www.lab-initio.com/ Announcements LEAD/tutoring sessions are good for verifying your mastery of the assigned homework: http://lead.mst.edu/ http://studentsuccess.mst.edu/tutoring/ http://lead.mst.edu/assist/index.html If I say “click on the link shown…” during a video lecture, what I really mean is “run the Powerpoint and click on the link there, or else type the link by hand.” Announcements Other help: Disability Support Services (accommodation letters) http://dss.mst.edu/ Counseling Center http://counsel.mst.edu/ Testing Center http://testcenter.mst.edu/ Announcements Exam 1 is Tuesday, February 16, from 5:00-6:00 PM. According to the Student Academic Regulations “The period from 5:00 – 6:00 PM daily [is] to be designated for common exams. If a class or other required academic activity is scheduled during common exam time, the instructor of the class that conflicts with the common exam will provide accommodations for the students taking the common exam.” E-mail me by the end of Friday of next week if for some reason you have a non-class-related time conflict for Exam 1 (5:006:00 pm, Tuesday, February 16). Include in your email your recitation section letter and the details of your circumstance. (That doesn’t mean I accept responsibility for fixing the conflict.) Announcements Exam 1 is Tuesday, February 16, from 5:00-6:00 PM. The fall Career Fair is also February 16. The exam starts well after scheduled Career Fair activities have ended. If you have an interview or MUST attend a Career Fair activity during your recitation time on February 16, contact your recitation instructor. In such a case, you may wish to attend a recitation at a time other than your scheduled time. It is unlikely that Career Fair activities will conflict with the 5-6 PM exam time, but if there is such a conflict, e-mail me the details as soon as you find out about it. We understand the importance of the career fair and will work with you to make sure you can participate! Announcements Homework for tomorrow: 21: 51, 79ab, 82ab, 85, 90 (reminder: all solutions must begin with starting equations) You only need to do parts a and b of problem 79. You don’t need to be paranoid about using Official Starting Equations (OSE’s), but don’t start a problem with a “random” equation from your book. Exception: if you have been given permission to start a problem with an equation that is not an OSE. Announcements If a homework problem asks for the magnitude and direction of a vector, we are usually satisfied if you provide its components, or express it in unit vector notation. You might want to be paranoid and verify beforehand that this is OK. Announcements Labs begin this week. If you have lab this week, don’t miss it! 3L01 is “odd” 3L02 is “even” “Odd” labs meet this week (3L01, 3L03, 3L05, etc.). “Even” labs meet the week of February 1. You will need to purchase a lab manual. Go to the department office, room 102, to purchase your lab manual! The cost is $25.00. Do not ask me for a lab manual; I do not have them! Students not purchasing a lab manual will receive a lab grade of zero. Lab manuals are not available at the bookstore. http://campus.mst.edu/physics/courses/2135lab/ The Big Picture, Part I In Lecture 1 you learned Coulomb's Law: 1 q1q 2 F = , 2 12 4πε 0 r12 r12 + - Q1 Q2 Coulomb’s Law quantifies the force between charged particles. The Big Picture, Part II In Lecture 1 you also learned about the electric field. There were two kinds of problems you had to solve… The Big Picture, Part IIa 1. Given an electric field, calculate the force on a charged particle. F E= q F= qE - F E You may not be given any information about where this electric field “comes from.” Or: given the force on a charged particle, determine the electric field that caused the force. The Big Picture, Part IIb 2. Given one or more charged particles, calculate the electric field they produce. We’ll focus on this topic today. q E=k 2 r q E=k 2 rˆ r I strongly recommend you start with this and do x and y components separately. Avoid for now. These are examples of “legal” equations: F = qE F E= q F= q E F E= q F This is INCORRECT: q = E F = q E F F q = E E (do you know why?) F This is POSSIBLY INCORRECT: q = (do you know why?) E q = F/E works *IF* q is positive. It is safer to write |q| = F/E. Today’s agenda: The electric field due to a charge distribution. You must be able to calculate electric field of a continuous distribution of charge.