**April 15, 1999 1:31 pm**

From: "Winters, Loren" <winters@academic.ncssm.edu>To: Dahl Clark <ClarkD@academic.ncssm.edu>, Danny Leung <LeungD@academic.ncssm.edu>, Daren Zou <ZouD@academic.ncssm.edu>,Maritza Hobson <HobsonM@academic.ncssm.edu>, Rashmi Patel <PatelR@academic.ncssm.edu>, Steven Carpenter <CarpenterS@academic.ncssm.edu>, Trajan DOgny <DognyT@academic.ncssm.edu>, Zachary Keane <KeaneZ@academic.ncssm.edu>Subject: 32-36Date: Thu, 15 Apr 1999 13:31:43 -0400

PH211 Students, Please stop by to pick up last Tuesday's homework. Everyone needs to do at least a bit (in some cases, a lot) of rework on 32-36. Here are some pointers: In part a, several people invented new physics by using the wrong formula for B and then integrating B over r, the distance from the wire. What you should integrate is the dot product of B and da. And note that B is not a constant that you can take out of the integral! Substitute the correct formula for B for a long, straight wire, pick a relevant area element, and integrate. (Daren did this on the board Wednesday.) In part d, I saw two methods. Some people found force using ilxB. The question that arises is what value of B do you use, since B depends on distance from the wire. Other people found force using F = P/v, the value of P coming from part c. Some then went on to calculate P in part e using the same formula rearranged, P = Fv. Of course, when they compared the result to part c, the answers were identical. Duh. You need a method other than F = P/v to find F in order to avoid this circular trap. Remembering that what you need is an average force, integrate ilxB over the width of the loop and divide the result by the width. It works! Rework on this problem will be due Monday at 5 PM. LW

April 22, 1999 2:25 pm

From: "Clark, Dahl" <ClarkD@academic.ncssm.edu>To: "'clarkdbc@hotmail.com'" <clarkdbc@hotmail.com>Subject: testDate: Fri, 30 Apr 1999 17:50:36 -0400 -----Original Message----- From: Winters, Loren To: Dahl Clark; Danny Leung; Daren Zou; Maritza Hobson; Rashmi Patel; Steven Carpenter; Trajan DOgny; Zachary Keane Sent: 4/22/99 2:25 PM Subject: test PH211 Students, Your tests are checked. In view of the fact that we don't meet until Tuesday and you need the whole period for your lab and I won't be in class Wednesday, I recommend that you pick up your test from my office. LW

April 22, 1999 2:25 pm

From: "Clark, Dahl" <ClarkD@academic.ncssm.edu>To: "'clarkdbc@hotmail.com'" <clarkdbc@hotmail.com>Subject: testDate: Fri, 30 Apr 1999 17:50:36 -0400 -----Original Message----- From: Winters, Loren To: Dahl Clark; Danny Leung; Daren Zou; Maritza Hobson; Rashmi Patel; Steven Carpenter; Trajan DOgny; Zachary Keane Sent: 4/22/99 2:25 PM Subject: test PH211 Students, Your tests are checked. In view of the fact that we don't meet until Tuesday and you need the whole period for your lab and I won't be in class Wednesday, I recommend that you pick up your test from my office. LW

April 26, 1999 11:03 am

From: "Clark, Dahl" <ClarkD@academic.ncssm.edu>To: "'clarkdbc@hotmail.com'" <clarkdbc@hotmail.com>Subject: FW: TuesdayDate: Fri, 30 Apr 1999 17:50:52 -0400

-----Original Message----- From: Winters, Loren To: Dahl Clark; Danny Leung; Daren Zou; Maritza Hobson; Rashmi Patel; Steven Carpenter; Trajan DOgny; Zachary Keane Sent: 4/26/99 11:03 AM Subject: Tuesday For lab tomorrow, let's not use lab books. You'll record all your data, method descriptions, and calculations on notebook paper (in pen, of course). I recommend formatting your report in advance, leaving plenty of space for information that you will add during the lab. LW

**April 30, 1999 3:34 pm**

From: "Winters, Loren" <winters@academic.ncssm.edu>To: "Clark, Dahl" <ClarkD@academic.ncssm.edu> CC: "'lmwinters@msn.com'" <lmwinters@msn.com>Subject: SaturdayDate: Fri, 30 Apr 1999 15:34:09 -0400

Dahl, Are we still planning to work on your project Saturday afternoon? If so, let's meet around 1 PM. Let me know if that's OK with you. (Just reply to all users and I'll get your message at home.) LW