tag:blogger.com,1999:blog-74429096067794447482024-03-06T02:51:05.316-06:00Physics 126Honors Physics II at UApleclairhttp://www.blogger.com/profile/07263994015241270268noreply@blogger.comBlogger190125tag:blogger.com,1999:blog-7442909606779444748.post-40992443299058394862011-12-19T02:48:00.002-06:002011-12-19T02:48:51.512-06:00Grades<div dir="ltr" style="text-align: left;" trbidi="on">
I have just finished grading the final exams, and the average was about 82%. I was pretty happy with how it came out, and most of you didn't end up changing your grade going into the final exam by very much. I should have your grades posted Monday evening some time, and will try to email each of you a grade breakdown as well. </div>pleclairhttp://www.blogger.com/profile/07263994015241270268noreply@blogger.com0tag:blogger.com,1999:blog-7442909606779444748.post-74372062542159209642011-12-14T13:49:00.000-06:002011-12-14T13:49:46.980-06:00Final project videos<div dir="ltr" style="text-align: left;" trbidi="on">
<br />
All the final projects finished up nicely, and we have video and code for all of them. So, in case you want to try them out, here is some information:<br />
<br />
<b>4 bit maze [Daniel Jenkins, Andrew Wagner]:</b><br />
<br />
Mr. Jenkins and Mr. Wager implemented the Arduino four bit maze found <a href="http://www.cs.gettysburg.edu/~tneller/mazes/oskar4bit/">here</a>, and explain their project in <a href="http://www.youtube.com/watch?v=3sHXcicMyn0&list=LLH7yfwYxwSPag9QK2_w999g&index=2&feature=plpp_video">this video</a>.<br />
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<b>d-pad/joystick controlled Etch-a-Sketch [Coston Rowe, Andrew Hicks, David Thompson]:</b><br />
<br />
Mr. Rowe, Mr. Hicks, and Mr. Thompson used <a href="http://www.parallax.com/tabid/768/ProductID/102/Default.aspx">Parallax servo motors</a> and a homemade joystick/d-pad to remotely draw on an etch-a-sketch. Their Arduino code is <a href="http://faculty.mint.ua.edu/~pleclair/ph126/Labs/final_projects_F11/Etch_Sketch.pde">here</a>, and they describe their work in <a href="http://www.youtube.com/watch?v=Cf9vZ6Vmwfo&list=LLH7yfwYxwSPag9QK2_w999g&index=3&feature=plpp_video">this video</a>.<br />
<br />
<b>Daft punk helmet [Jacob Moxley, Cameron Darling]:</b><br />
<br />
Mr. Moxley and Mr. Darliny used an Arduino Uno and the <a href="http://jimmieprodgers.com/kits/lolshield">LoLShield</a> they assembled to create a Daft Punk-inspired helmet with scrolling messages. Their code was based on cibomahto’s <a href="https://github.com/cibomahto/LoLShield">LoLShield library</a>, <a href="http://faculty.mint.ua.edu/~pleclair/ph126/Labs/final_projects_F11/daft_LoL/">with some modifications to fix lower-case letter display and implement sprite-style graphics</a>. They describe their work <a href="http://www.youtube.com/watch?v=eGqzzENS-N0">in this video</a>.<br />
<br />
<b>RFID tunes [Ali Cortez, Max Peeples]:</b><br />
<br />
Mr. Cortez and Mr. Peeples implemented a tune generator based on reading RFID cards that encode pitches, notes, rests, etc. Their code and all project details <a href="http://faculty.mint.ua.edu/~pleclair/ph126/Labs/final_projects_F11/rfid-tunes/">are here</a>, and they describe their work in <a href="http://www.youtube.com/watch?v=ZWX0_zUAteI&feature=youtube_gdata_player">this video</a>.<br />
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<b>“Incredimen” pseudo-Theremin [David Gillespie, Derek Brazzell]</b><br />
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Finally, Mr. Gillespie and Mr. Brazzel made a pseudo-<a href="http://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0CFQQFjAA&url=http%3A%2F%2Fen.wikipedia.org%2Fwiki%2FTheremin&ei=CP3oTr35LcbqtgfR6czYCg&usg=AFQjCNHr5BALJjmfE2z26j1PPUoKyysszg">Theremin</a>. The main differences from a traditional Theremin are the use of lower frequency oscillators (~80kHz) to make things easier, and using a op-amp simple summing circuit for multiplexing rather than a more complicated mixer. The use of lower frequencies does impact the sensitivity, but it still works great and sounds very, very weird. They describe their work in <a href="http://www.youtube.com/watch?v=NrpbqFh6CWs&feature=g-upl">this video</a>, which apparently they spent quite a bit of time on!<br />
<br />
If you want more project details, you can contact me and I'll either tell you what I know or put you in touch with the students who did the project.</div>pleclairhttp://www.blogger.com/profile/07263994015241270268noreply@blogger.com0tag:blogger.com,1999:blog-7442909606779444748.post-52803296912927187732011-12-13T01:52:00.002-06:002011-12-13T01:58:14.945-06:00Final exam hints<div dir="ltr" style="text-align: left;" trbidi="on">
The final exam is really difficult. My wife asked me if it was difficult because you all hadn't studied enough or something, and my reply was "no, they have studied, it is just really difficult." Then I decided I should probably help get you started a little bit ...<br />
<div>
<br /></div>
<div>
Even with massive hints, some of them are still very hard (or messy, or both). They are more open-ended problems than you are probably used to, requiring approximations or assumptions that you have to come up with on your own to generate reasonable solutions. With one exception, not the sort of problems where you just identify formulas or set up an integral or two. If there is a lesson here, I guess it is that realistic problems are messy and difficult, and half the time you don't even know where to start. The trick is to figure out how to make it look <i>approximately</i> like one of the nice tidy textbook problems, without sacrificing too much in the way of accuracy or realism.</div>
<div>
<br /></div>
<div>
Anyway: <a href="http://faculty.mint.ua.edu/~pleclair/ph126/Exams/final_hints.pdf">here are the massive hints I spoke of</a>. I also corrected a typo in number 4 - it should be "b/a" in the log, not "a/b".</div>
</div>pleclairhttp://www.blogger.com/profile/07263994015241270268noreply@blogger.com0tag:blogger.com,1999:blog-7442909606779444748.post-37604003834860531342011-12-12T01:17:00.001-06:002011-12-12T01:18:00.130-06:00Your final exam<div dir="ltr" style="text-align: left;" trbidi="on">
<a href="http://faculty.mint.ua.edu/~pleclair/ph126/Exams/PH126_final_F11.pdf">Here you go</a>. Feel free to ask questions about the problems if something seems unclear, or you don't know how to get started. I'll clarify what I can without giving away too much ...</div>pleclairhttp://www.blogger.com/profile/07263994015241270268noreply@blogger.com0tag:blogger.com,1999:blog-7442909606779444748.post-2443308336667425092011-12-09T13:02:00.001-06:002011-12-09T13:03:16.919-06:00Dell laptop cord left in lab<div dir="ltr" style="text-align: left;" trbidi="on">
I found a stray Dell laptop power cord in the lab after class today. I'll bring it to the main office (206 Gallalee), if it is yours you can drop by to claim it from 9-12, 1-4:45 any weekday.</div>pleclairhttp://www.blogger.com/profile/07263994015241270268noreply@blogger.com0tag:blogger.com,1999:blog-7442909606779444748.post-34670835843423482742011-12-07T16:03:00.001-06:002011-12-07T16:04:38.147-06:00Continuing your projects<div dir="ltr" style="text-align: left;" trbidi="on">
Just a thought: if any of you need PH elective credit, and would like to continue to refine and complexify your final projects (or something else), I'd be happy to work with you next semester via an independent study course. If this sounds like something interesting, let me know and we can talk about the details.</div>pleclairhttp://www.blogger.com/profile/07263994015241270268noreply@blogger.com0tag:blogger.com,1999:blog-7442909606779444748.post-38022738807633712072011-12-06T01:30:00.001-06:002011-12-06T02:38:34.774-06:00Final projects and "report"<div dir="ltr" style="text-align: left;" trbidi="on">
Well, everyone's project basically works. Most of you have a little polishing to do, but the basic idea worked out for everyone, and you managed to build some pretty cool stuff. It would be a shame if this information were lost, right?<br />
<br />
Keeping that in mind, and the fact that <a href="http://en.wikipedia.org/wiki/Streisand_effect">nothing can really be deleted from the internet</a>, I've decided to change the final reporting requirements. In your favor, as it were. Rather than writing a final report at this late date, I want you all to make short videos describing your project, along with a demonstration of how it works. There are no real restrictions, just a few guidelines & suggestions:<br />
<br />
<ul style="text-align: left;">
<li>You don't have to be on camera yourselves, just your project. You do have to speak though.</li>
<li>A few minutes is enough, if you can describe the project well enough</li>
<li>You should briefly describe the point of the project, showing diagrams or schematics as necessary (say, on the blackboard or a sheet of paper) so it is clear how you made it work</li>
<li>Describe the hardware and code required to make it work, in brief. Include links with the video to make this easier (see below).</li>
<li>End with a live demo of the project, showing its basic functionality, operation, and major components</li>
<li>Upload to YouTube or your preferred time sink</li>
<li>If you made heavy use of particular web pages (e.g., schematics, code, etc), send me those links.</li>
<li>The video + links should be enough for a reasonably proficient tinkerer to reproduce your project.</li>
<li>Do plan a short script or sketch of what you want to do for your video, it will not go well if you just start shooting and rambling at the camera :-)</li>
</ul>
<br />
I'll post links to the videos here, along with files of any schematics/code you think is non-obvious. The basic idea is that should someone like yourselves search for a similar project, they'll find your video and any interesting supplemental information required to make it work. Maybe then they will have an easier time doing it themselves, or at least be inspired to try it out, having seen it is possible. Many of you came up with your projects this way, so you'll be paying it forward a bit.<br />
<br />
During Wednesday & Friday's classes, I'll bring in my camera, phone, and laptop (all of which take video), or you can use your own phones/laptops/etc. There should be enough time during those two class periods for most of you to complete your short videos, or we can work out another time for you to come in and do it outside of class if you like. For that matter, if your project is portable, you can do it in your dorm room.<br />
<br />
So, all you really need to do for your projects at this point is (1) polish as you see fit, (2) take a video, (3) turn in any code/schematics/links/etc to include as supplemental information with the video.<br />
<br />
Grading will count one lab report grade each for: (1) video quality/clarity/etc, (2) functionality of the project (how well it worked), (3) overall polish of the completed project (hardware & code), (4) creativity in coming up with and implementing the project. That means the final project is just under half your lab grade, which is itself 15% of your overall grade. It is a group grade, each team member gets the same grade for the final project.<br />
<br />
More details and discussion in Wednesday's class.</div>pleclairhttp://www.blogger.com/profile/07263994015241270268noreply@blogger.com0tag:blogger.com,1999:blog-7442909606779444748.post-42464000577812314692011-12-02T01:53:00.001-06:002011-12-02T01:56:12.231-06:00Notes on EM waves, radiation, etc<div dir="ltr" style="text-align: left;" trbidi="on">
<a href="http://faculty.mint.ua.edu/~pleclair/ph126/Misc/Notes/radiation_EM-waves.pdf">Here are some notes</a> on radiation, EM waves in conductors and insulators, etc - the stuff we've been covering the last several lectures. They are rather long, and incomplete in places ... but they do cover some interesting things I didn't quite get time to go over in lecture.<br />
<br />
The first part is deriving the radiated power by accelerating charges, and applying that to several systems (oscillating charges, circular motion, etc.). The second part is deriving the blackbody radiation, which we did not cover (you'll see this in PH253). The last part is EM waves in solids, complex conductivity and dielectric functions derived from a model of oscillating charges. An appendix shows how to derive B from E in a moving reference frame.</div>pleclairhttp://www.blogger.com/profile/07263994015241270268noreply@blogger.com0tag:blogger.com,1999:blog-7442909606779444748.post-53301823329927810132011-11-29T12:13:00.001-06:002011-11-29T12:13:49.159-06:00There will not be any further HW.<div dir="ltr" style="text-align: left;" trbidi="on">
Given that next week is dead week and you have an exam on Friday, we'll call it quits at 8 homework sets. Christmas comes early this year ;-)</div>pleclairhttp://www.blogger.com/profile/07263994015241270268noreply@blogger.com0tag:blogger.com,1999:blog-7442909606779444748.post-45128098046815499132011-11-29T01:58:00.001-06:002011-11-29T02:07:49.441-06:00Exam 3<div dir="ltr" style="text-align: left;" trbidi="on">
The coverage for exam 3 on Friday will be:<br />
<br />
<ul style="text-align: left;">
<li>magnetic fields (2 problems; Ch. 28.2-4, 6, 8-10; 29.2-6)</li>
<ul>
<li>motion of charges in magnetic fields</li>
<li>fields due to current-carrying wires (Ampere, Biot-Savart)</li>
</ul>
<li>induction (2 problems; Ch. 30.2-8)</li>
<ul>
<li>motionally-induced voltage</li>
<li>Faraday's law </li>
</ul>
<li>ac circuits (1 problem; Ch. 31.2-9)</li>
<ul>
<li>filters</li>
<li>impedance</li>
</ul>
</ul>
<br />
Nothing on op-amps/transistors/comparators, Maxwell's equations, EM waves, or relativity for this exam, though some of that may show up on the final. Similar to the homework problems, but less involved. Out of the 5 problems, you will have to choose 3 to solve, so the odds are not bad. You'll have 50 minutes for the exam. I'll provide a basic formula sheet with everything you really need, and you can bring in one sheet of your own.<br />
<br />
I'll try to provide some more details on Wednesday in class, but feel free to remind me or ask some questions. I will really try not to make it too difficult ...</div>pleclairhttp://www.blogger.com/profile/07263994015241270268noreply@blogger.com0tag:blogger.com,1999:blog-7442909606779444748.post-40834730436051733982011-11-28T13:19:00.001-06:002011-11-28T13:21:09.211-06:00New Spring courses<div dir="ltr" style="text-align: left;" trbidi="on">
<br />
<div class="p1">
We have two brand-new never-before-offered courses this spring you might want to consider:</div>
<div class="p1">
<br /></div>
<div class="p1">
<a href="http://physics.ua.edu/courses/AY/AY155/AY155-LifeUniv-2012Spring-Silverstone.pdf">AY 155 - Life in the Universe</a> (Silverstone)</div>
<div class="p1">
<a href="http://physics.ua.edu/courses/PH/PH482-582/PH482-Metaphysics-2012Spring-LeClair.pdf">PH 482 / PHL 480 - Physics & Metaphysics</a> (LeClair / Hestevold)</div>
<div class="p1">
<br /></div>
<div class="p1">
Links go to course syllabi, let me know if you want any more information.</div>
</div>pleclairhttp://www.blogger.com/profile/07263994015241270268noreply@blogger.com0tag:blogger.com,1999:blog-7442909606779444748.post-69327722602943690942011-11-28T13:11:00.001-06:002011-11-28T13:12:14.023-06:00Course evaluations<div dir="ltr" style="text-align: left;" trbidi="on">
It is that time again ... please remember to do your online course evaluations. I won't see them until well after final grades are due.<br />
<br />
<blockquote>
This course will be using an online system for collecting the end-of-semester Student Opinions of Instruction questionnaires. Your response is very important and is used to assess curricular and instructional quality, as well as to identify opportunities for improvement. The online system enables you to: </blockquote>
<blockquote>
<br />
<ul style="text-align: left;">
<li>complete the questionnaire anytime, anywhere, at your own pace allowing for more thoughtful and constructive responses</li>
<li>save and return later, as well as review and edit responses prior to submitting</li>
<li>responses are confidential; only a summary of all student responses will be provided to your instructors and administrators.</li>
<li>For more information about this process, go to <a href="http://oira.ua.edu/soi/soi_info.html"><span class="s1">http://oira.ua.edu/soi/soi_info.html</span></a>.</li>
<li>Beginning November 28, 2011, the Student Opinions of Instruction questionnaires will be available. You may access them as follows:</li>
<li>Login to myBama and select the “Your opinions matter!” image on the Student tab. Once in the system, you will see a list of courses you are being asked to evaluate.</li>
<li>An invitation containing a link to login will be sent to your Crimson account. Up to 3 reminders will be sent; reminders will only be sent to those who have not submitted all questionnaires for all courses.</li>
</ul>
</blockquote>
</div>pleclairhttp://www.blogger.com/profile/07263994015241270268noreply@blogger.com0tag:blogger.com,1999:blog-7442909606779444748.post-87719228950043519972011-11-17T22:53:00.001-06:002011-11-17T22:54:41.211-06:00HW8 hints<div dir="ltr" style="text-align: left;" trbidi="on">
Problem 6 is a bit sneaky. Think about how the capacitance relates to the geometry of the capacitor (C ~ A/d), and how those distances are contracted. If you move toward the plates along the axis, the plate spacing is contracted, but area remains the same. If you move perpendicular to the axis, the spacing is the same, but what happens to the surface charge density?<br />
<div class="p2">
<br /></div>
<div class="p1">
As one hint, charge is invariant, and always the same no matter what relative motion there is.</div>
<div class="p2">
<br /></div>
<div class="p1">
As a stronger hint, I was about to post <a href="http://faculty.mint.ua.edu/~pleclair/PH253/Notes/blackbody.pdf">my notes on radiation</a>, which starts out with the fields of moving charges ... </div>
<div class="p2">
<br /></div>
<div class="p1">
For 7, note that F = qE = dp/dt, with momentum p=(gamma)mv. Then</div>
<div class="p2">
<br /></div>
<div class="p1">
dp/dt = (gamma) m dv/dt + mv d(gamma)/dt</div>
<div class="p2">
<br /></div>
<div class="p1">
With the definition of gamma, grind through the derivatives and it should work out.</div>
<div class="p1">
<br /></div>
<div class="p1">
I'm going to run through #6 and 7 tomorrow in class in any event, just to make sure you know how to get started.</div>
</div>pleclairhttp://www.blogger.com/profile/07263994015241270268noreply@blogger.com0tag:blogger.com,1999:blog-7442909606779444748.post-30605680461651464882011-11-15T01:37:00.001-06:002011-11-15T01:53:25.788-06:00Final project parts have mostly arrived<div dir="ltr" style="text-align: left;" trbidi="on">
Most of your stuff is in, I think we're only waiting on the multiplying chip, which should arrive on Tuesday. Here are some details about what I've got ...<br />
<br />
<a name='more'></a><br />
1) I received a package of 160 assorted LEDs, and <a href="https://www.adafruit.com/products/493">3 of the 9x14 arrays</a>. Some assembly is required:<br />
<div class="separator" style="clear: both; text-align: center;">
<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhYCQKI1iNxBWpFzA9-19d-L0ofgLVslWY8hLr5piP_t71h85WRqv-hLX4nGVxMKQNtNXcSFe_jtbSViGOMgRB51dvBKYvSwXSnhri0_9fPqjFpuf9b7BQLsKweXe1QdurAnk6rB0Jtzz8/s1600/charlieplex.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="179" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhYCQKI1iNxBWpFzA9-19d-L0ofgLVslWY8hLr5piP_t71h85WRqv-hLX4nGVxMKQNtNXcSFe_jtbSViGOMgRB51dvBKYvSwXSnhri0_9fPqjFpuf9b7BQLsKweXe1QdurAnk6rB0Jtzz8/s320/charlieplex.png" width="320" /></a></div>
I have been soldering for some time now ... but I should have at least one of them ready to go by Wednesday's class. The 9x14 array plugs right into the Arduino board, then you can program it to display what you like.<br />
<br />
2) The stepper motors are in. Stepper motors use what is called <a href="http://en.wikipedia.org/wiki/Pulse-width_modulation">pulse width modulation</a>, and are controlled by a digital output pin (they also require a +5V power and GND connection). The motor expects a pulse every 20ms, and the <i>width</i> of this pulse encodes the speed and direction. For <a href="http://www.google.com/url?sa=t&rct=j&q=parallax%20continuous%20rotation%20servo&source=web&cd=1&sqi=2&ved=0CCAQFjAA&url=http%3A%2F%2Fwww.parallax.com%2Fdl%2Fdocs%2Fprod%2Fmotors%2Fcrservo.pdf&ei=XhfCTvGWDsPLgQeA143YDg&usg=AFQjCNFsRgm0ialwHy4pVUGgiozdvUqU0A">these particular motors</a>, a pulse width of 1.5ms is "zero", and positive and negative deviations from that correspond to higher CW and CCW rotation speeds. For example, a 2.0ms pulse width is maximum CW rotation, and 1.0ms pulse width maximum CCW rotation. Here is some simple and quickly hacked-together code which illustrates two different controls: first start at maximum speed in one direction, gradually slow down, and then speed up in the other direction; then, at fixed speed (1.75ms pulse width), move through one full rotation (52 steps):<br />
<br />
<blockquote>
<span class="Apple-style-span" style="font-size: x-small;">//simple code to control a parallax continuous rotation stepper motor<br />int servo1 = 7, i=0;<br />int myAngle1;<br />int pulseWidth1;<br />void servoPulse1 (int servo1, int myAngle1) { //1.5 ms at 20ms intervals.<br /> pulseWidth1 = (myAngle1 ) + 1500; // Converts angle to microseconds<br /> <br /> digitalWrite(servo1, HIGH); // Set servo high (turns it on)<br /> delayMicroseconds(pulseWidth1); // Wait a very very small amount<br /> digitalWrite(servo1, LOW); // Set servo low (turns it off)<br /> <br /> delay(20); // Refresh cycle of servo (20 ms)<br />}<br />void setup() {<br /> pinMode(servo1, OUTPUT);<br />}<br />void loop() {<br /> <br /> for (myAngle1=-500; myAngle1<=500; myAngle1++) { //fast in one dir; slow down, reverse, speed up<br /> servoPulse1(servo1, myAngle1);<br /> }<br /> <br /> delay(1000);<br /> <br /> myAngle1=250; //set a meduim speed in one direction<br /> <br /> for (i=0; i<52; i++) { //now just move some pulses in one direction at fixed speed<br /> servoPulse1(servo1,myAngle1); //seems to be ***52*** pulses per rotation<br /> }<br /> <br /> delay(1000);<br />}</span></blockquote>
With the Arduino boards you have, it is no problem to control several stepper motors. Working from this code, you should be able to figure out how to control the motors nicely.<br />
<br />
3) I found an old Commodore joystick I made in college, as well as some third party Commodore/Atari joysticks. Yes, I have such things just lying around my garage, and I really did make my own joystick for fun ...<br />
<br />
4) I have an Etch-a-Sketch we can use, but it is in tough shape. I'll get a better one, but we have at least something to start with.<br />
<br />
5) I have a transistor-based Colpitts oscillator completed and in a project box to use as a either the fixed or variable oscillator for a Theremin. It is a design I fiddled with over the summer that has somewhat improved frequency stability over the <a href="http://en.wikipedia.org/wiki/Colpitts_oscillator">basic Colpitts design</a>, probably it is better for the reference oscillator. Here's a schematic, which I can explain when we're in the lab next:<br />
<br />
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<a href="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEie4YtnP7qyW-OqLGsFQZuPvJaZ1mixaRuouilScV2cmHEIQ8fBOpPOXaPLxzm-t-NWKuQfeuB0gVqTOeik83XR_fPHUMooC2hnUI9PLfs49IKmsA56y1_JrPl57qjB2Nf9OIs3K2zk8Sk/s1600/mod-colpitts.png" imageanchor="1" style="margin-left: 1em; margin-right: 1em;"><img border="0" height="226" src="https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEie4YtnP7qyW-OqLGsFQZuPvJaZ1mixaRuouilScV2cmHEIQ8fBOpPOXaPLxzm-t-NWKuQfeuB0gVqTOeik83XR_fPHUMooC2hnUI9PLfs49IKmsA56y1_JrPl57qjB2Nf9OIs3K2zk8Sk/s320/mod-colpitts.png" width="320" /></a></div>
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</div>pleclairhttp://www.blogger.com/profile/07263994015241270268noreply@blogger.com0tag:blogger.com,1999:blog-7442909606779444748.post-71007034191154333732011-11-14T15:27:00.001-06:002011-11-14T15:28:50.845-06:00Relativity notes<div dir="ltr" style="text-align: left;" trbidi="on">
We're covering relativity right now, and obviously it is not in your book. <a href="http://faculty.mint.ua.edu/~pleclair/ph102/Notes/ph102_notes.pdf">I will be following my own notes here</a>. See Ch. 1 for relativity, treat it as the missing chapter in your textbook that really should have been included.<br />
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You should also check out the chapter on magnetism (Ch. 7, iirc), it contains a simplified derivation of the magnetic field from the electric field in a moving reference frame.</div>pleclairhttp://www.blogger.com/profile/07263994015241270268noreply@blogger.com0tag:blogger.com,1999:blog-7442909606779444748.post-31948730117977790492011-11-10T14:12:00.003-06:002011-11-10T14:12:26.010-06:00Final project parts<div dir="ltr" style="text-align: left;" trbidi="on">
Having not heard much yet, I went ahead and ordered a few things for the final projects that I guessed you would probably need or could use:<br />
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<ul style="text-align: left;">
<li>160 assorted LEDs</li>
<li>3 of <a href="https://www.adafruit.com/products/493">these 9x14 LED blocks</a> (red, green, blue)</li>
<li>3 <a href="http://www.adafruit.com/products/154">continuous rotation motors</a></li>
<li><a href="http://www.analog.com/en/special-linear-functions/analog-multipliersdividers/ad835/products/product.html">a multiplying chip </a>for constructing the theremin</li>
<li>20 <a href="http://www.parallax.com/Store/Accessories/CommunicationRF/tabid/161/CategoryID/36/List/0/SortField/0/Level/a/ProductID/115/Default.aspx">125kHz EM41000 RFID tags</a></li>
</ul>
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Most of this stuff should arrive by Monday, all of it should be here by Wednesday. We may need some other parts yet (which you should specify ...), but this should be enough to get us started.<br />
<br /></div>pleclairhttp://www.blogger.com/profile/07263994015241270268noreply@blogger.com0tag:blogger.com,1999:blog-7442909606779444748.post-35257178646089091882011-11-09T07:56:00.000-06:002011-11-09T07:56:05.991-06:00Today:<div dir="ltr" style="text-align: left;" trbidi="on">
a reminder that you will have a lab day today, no lecture. You can show up at the lab directly at 11:00. I have an appointment in Birmingham this morning, and will probably not make it back at all, though I will try to catch the end of the class. Your undergrad assistant will be there, and I arranged to have the room opened at 11:00.<div>
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Your main goals today, if nothing else, are (1) better define your final project, getting down to some of the details of what you are going to do, (2) come up with a list of (at least preliminary) items you will need me to procure.</div>
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In particular, if you need me to buy stuff (like LEDs, RFID cards, etc) I need to know that ASAP so I can have it by next week.</div>
</div>pleclairhttp://www.blogger.com/profile/07263994015241270268noreply@blogger.com0tag:blogger.com,1999:blog-7442909606779444748.post-22828209749065103152011-11-08T16:51:00.005-06:002011-11-08T16:51:43.912-06:00HW8 is out<div dir="ltr" style="text-align: left;" trbidi="on">
<a href="http://faculty.mint.ua.edu/~pleclair/ph126/Homework/HW8_ind_18Nov11.pdf">Covers ac circuits mostly</a>, with a couple of relativity questions thrown in (we'll get to that next week). Due next Friday.<div>
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Should have HW7 solutions out this evening ...</div>
</div>pleclairhttp://www.blogger.com/profile/07263994015241270268noreply@blogger.com0tag:blogger.com,1999:blog-7442909606779444748.post-60660422490297808462011-11-03T00:12:00.001-05:002011-11-03T00:12:17.464-05:00Next HW<div dir="ltr" style="text-align: left;" trbidi="on">
HW8 will probably come out Thursday, covering mostly ac circuits, and it will not be due until something like next Friday. I got a little delayed making it up today ... it should be a bit shorter than the last couple.</div>pleclairhttp://www.blogger.com/profile/07263994015241270268noreply@blogger.com0tag:blogger.com,1999:blog-7442909606779444748.post-1668862978838534562011-11-02T01:20:00.002-05:002011-11-02T10:40:54.204-05:00Remaining Schedule<div dir="ltr" style="text-align: left;" trbidi="on">
We're down to about a month to go now, and here's what I have planned lecture-wise:<br />
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2 Nov: induction, ac circuits<br />
4 Nov: mutual inductance, ac circuits more so (HW8 comes out)<br />
7 Nov: filters, EM waves<br />
9 Nov: lab day/work on final projects<br />
11 Nov: electricity and magnetism in real materials (HW8 due, HW9 out)<br />
14,16 Nov: relativity<br />
18 Nov: radiation & light<br />
21 Nov: ray optics (HW9 due, HW 10 out)<br />
28 Nov: lenses, mirrors<br />
30 Nov: wave optics (HW 10 due, last one)<br />
2 Dec: Exam 3 (induction, ac circuits, ray optics)<br />
5, 7, 9 Dec (dead week): various sundry topics not on the final, concept assessment test (not graded).<br />
Before 16 Dec: take-home final due (cumulative)<br />
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Lab-wise, we'll be beginning final projects tomorrow (Wed). The idea is that you, as groups, will pick final circuit construction projects to work on for the rest of the semester. We will discuss this more tomorrow, but a few examples might be:<br />
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<ul style="text-align: left;">
<li><a href="http://en.wikipedia.org/wiki/Theremin">Theremin</a></li>
<li><a href="http://www.engadget.com/2011/10/05/arduino-ipod-and-rfid-make-beatiful-handicapped-accesible-musi/">RFID iPod control</a></li>
<li>audio distortion circuits (e.g. guitar pedals)</li>
<li>motor positioning control (e.g., simple robot)</li>
<li>Arduino multimeter (measure R, C, L with the Arduino)</li>
<li>Remote control </li>
<li>Home alarm system</li>
<li>Implementation of digital logic (basic computation)</li>
<li>LED display (8x8 grid, for example, displaying alphanumeric characters)</li>
<li>Something like <a href="http://hacknmod.com/hack/top-40-arduino-projects-of-the-web/">these</a> or <a href="http://www.arduino.cc/playground/Projects/ArduinoUsers">these</a></li>
</ul>
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It is open ended, in principle you can choose anything you like that (a) isn't dangerous, (b) I think you can pull off in 3-4 weeks, (c) isn't too simple, and (d) doesn't just implement an existing project you found online, but adds a new element. Think of it as a chance to try out any crazy, weird hack you've seen on the internet and get credit for it. You will have to decide quickly (in the next few days). You have available more or less any electronic components you like and the Arduino, so you might start by googling for interesting Arduino projects that you can embrace & extend.<br />
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You will have a few reporting requirements for the final projects, with "soft" deadlines:<br />
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6 Nov: 1 paragraph that gives a basic description of your project you have chosen<br />
8 Nov: more detailed project descriptions with a block diagram and possible parts I should procure<br />
16 Nov: 3 page memo describing the project, your initial design, and progress to date<br />
22 Nov: a second 3 page memo updating me on your progress to date<br />
28 & 30 Nov: final project work<br />
by 2 Dec: 3-5 page description of the project, how it worked out, and the final design.<br />
5-7 Dec (dead week): show your project off to your classmates (informal, not graded)<br />
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I should stress that I want you to be creative with the final projects, and err on the side of risk. It is not so important that you have a polished final product, it is more important that you try something complex that builds on what you've learned so far and come up with creative ideas. More bluntly, your final grade for the project will not depend so much on whether it worked flawlessly, but whether it was a good idea worth trying, and whether you had a workable approach to the thing.<br />
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If I deem your project workable, I will procure whatever parts are necessary within reason, so you need not worry about that. Assume an infinite budget until I tell you otherwise!<br />
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Finally, I will have nothing due during dead week. I anticipate your final projects being completed before dead week, and that last week there will be no homework, the lectures will not cover material relevant to the final exam, and the final project demonstrations will just be you showing off your neat hacks to your colleagues, ungraded.<br />
<br /></div>pleclairhttp://www.blogger.com/profile/07263994015241270268noreply@blogger.com0tag:blogger.com,1999:blog-7442909606779444748.post-73809233838352488322011-10-25T00:59:00.002-05:002011-10-25T00:59:50.019-05:00HW7 miscellanea<div dir="ltr" style="text-align: left;" trbidi="on">
Since we don't have class on Friday, I thought I'd post some HW hints. Keep in mind that the HW is due Mon 31 Oct at midnight, so we still have Monday's class to discuss the problems, i.e., I have not necessarily ruined your long weekend :-)<br />
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For problem 1, you know that motion of the L and R resistors leads to induced potential differences. That means it looks as though two little batteries are to be inserted into the circuit. But where? Faraday's law tells us that the integral of E.dl around a closed loop is the time rate of change of flux. The "loops" are defined by, say, the right resistor and the central one, and the left resistor and the central one. If the potential difference is non-zero when walking around one of these loops, the situation would be the same as if we just inserted infinitesimal batteries in the horizontal rails, one for each loop. Thinking about the direction of the induced currents tells you the orientation of each battery. This leaves you with a simple two-loop circuit.<br />
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For problem 2, you know the flux carved out by the moving rod is the integral of B.dA. B is just that of a wire at some distance r, no problem. dA is how much area is swept out in a time dt, which would be lvdt, making the integral one over time. Set up that integral, and its time derivative is the induced voltage. If you actually integrated anything, you missed something ...<br />
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Problem 3 has a nice story to it. It is a problem out of another common intro book (not the one we're using), and I thought it was cute. However, the solution that book gives is rather obtuse and not easily generalizable. In looking for a better way, I stumbled across the simple trick for plane curves given as a hint. As I showed in class today, it is easy to derive - write dl in polar coordinates, cross it into r-hat, and that's that. So long as the curve lies within a plane, and you want the field at some point within that plane, it works. It turns out there is a recent paper in the American Journal of Physics (a physics education journal) that derives the same formula and gives some nice examples. The derivation there is more geometrical, and probably easier to grok at first, but I sort of liked the elegance of the method I showed you. Anyway, <a href="http://ajp.aapt.org/resource/1/ajpias/v68/i3/p254_s1">the paper is worth a read</a>. [Download link will only work on campus.]<br />
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Problem 4 we just did in class. Think about this, though: the ring picks up angular momentum, though it started with none. That means the electromagnetic field must have contained some angular momentum that was imparted to the ring once we shut the field off!<br />
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For problem 5, think carefully about the direction of the induced currents in each resistor (presume the voltmeters draw no current, it as if they are not there). From Faraday's law you can find the magnitude of the current easily enough. Then since you know the voltage drops across a resistor by an amount IR, you can figure out the potential difference between b and a, which is what the voltmeter reads. Now think about this: the voltmeters are connected by perfect wires to the same points, but must read different values! How is that? It is because we have a time-varying B, and because the voltmeter measures the integral of E.dl over a given path. When B does not vary in time, E is conservative, and the path doesn't matter. When B *does* vary in time, E is not conservative, and the result of integrating E.dl, the voltage measured, depends on the path taken. It is a hard thing to get your head around.<br />
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Problem 6 we did in class. I will try to do the magnetic levitation of a superconductor (Meissner effect) demonstration before the end of the semester. Keep reminding me ...<br />
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Problem 7 we did in class. Someday, in a grad-level E&M class you may solve this problem directly using the cylindrical boundary conditions and Maxwell's equations, and it will be annoying and difficult (though exact). This way is limited in accuracy by your patience, but (I think) far more transparent. It was mainly included just to give you a physical picture for time-varying fields. There is a nice discussion in the <a href="http://en.wikipedia.org/wiki/The_Feynman_Lectures_on_Physics">Feynman lectures</a>, vol. 2, ch. 23 [If you a PH major, buy these books. There is a common copy in the physics student lounge.]</div>pleclairhttp://www.blogger.com/profile/07263994015241270268noreply@blogger.com0tag:blogger.com,1999:blog-7442909606779444748.post-46193996184368844622011-10-24T17:38:00.003-05:002011-10-24T17:38:31.207-05:00HW6 solutions<div dir="ltr" style="text-align: left;" trbidi="on">
<a href="http://faculty.mint.ua.edu/~pleclair/ph126/Homework/HW6_magn_14Oct11_SOLN.pdf">Here are some proposed solutions to HW6</a>. The circuit construction questions have many possible solutions, so if yours does not look like mine, don't worry too much.<br />
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<br /></div>pleclairhttp://www.blogger.com/profile/07263994015241270268noreply@blogger.com0tag:blogger.com,1999:blog-7442909606779444748.post-76602172400416891952011-10-21T00:37:00.001-05:002011-10-21T00:37:12.906-05:00HW7 out, due on halloween, appropriately.<div dir="ltr" style="text-align: left;" trbidi="on">
<a href="http://faculty.mint.ua.edu/~pleclair/ph126/Homework/HW7_ind_31Oct11.pdf">I don't think you'll like it at first</a>, but we will do at least two of the hardest problems in class. Keep in mind that halloween is the Monday following Fall break.</div>pleclairhttp://www.blogger.com/profile/07263994015241270268noreply@blogger.com0tag:blogger.com,1999:blog-7442909606779444748.post-75239765579497086142011-10-20T00:22:00.000-05:002011-10-20T00:22:11.454-05:00HW 4&5 solutions<div dir="ltr" style="text-align: left;" trbidi="on">
Long overdue, but HW 4&5 now have <a href="http://faculty.mint.ua.edu/~pleclair/ph126/Homework/">solutions</a>. Have a look, this stuff will come back again, if nothing else on the final exam. Some of it before then.</div>pleclairhttp://www.blogger.com/profile/07263994015241270268noreply@blogger.com0tag:blogger.com,1999:blog-7442909606779444748.post-34580382628604248822011-10-20T00:04:00.003-05:002011-10-20T00:04:45.202-05:00HW6 is a beast in fact.<div dir="ltr" style="text-align: left;" trbidi="on">
If you put it off until the last minute (i.e., right now) and tried to do it in one night, it isn't going to go well. You may want to ask for an extension, as it is likely to be given. This is important stuff, I'd rather you understand it a bit late than not at all. </div>pleclairhttp://www.blogger.com/profile/07263994015241270268noreply@blogger.com0