Attention: Optional Points available. As asked about in class, I said I could do a fun physics story on the morning of 5/14 at 9 AM. Those taking the AP test do not have to be in class that day, but they are welcome to come and hear the story. Those who show up at 9 AM, and do the little guiding worksheet I provide, can earn a 15 of 15. But you have to arrive at 9 AM to be eligible for these points. And if you're not taking the AP test, you have to come to class at 8 AM as usual. The idea of doing this came up in class on 5/8, but a resolution was never reached. I wasn't going to push it, but then a couple of interested people asked for it later in the day on 5/10. So we're doing it, and I'm using this medium to spread the word so everybody knows.

 

And a correction: I gave back some graded HW quiz, and on the 2006 question, Part e, I at first wasn't accepting Lenz's Law as a justification. But upon further thought, writing the answer "increases" on Part e and defending it with Faraday's Law could possibly be partially correct, depending on how the response is worded. If you think you might be eligible for this additional one point of credit, you can read my attachment here where I wrote "Correction" and see if your expressed idea matches. (Again, it only explains part of the phenomenon, and I do think my standard answer is more complete and efficient, but I'm happy to have the conversation if you wrote something relevant involving Faraday's Law. If you're in doubt, see the attachment.)

 

*Note: the version of the attachment that I delivered to people during 6th period on 5/10 did not at that time contain the correction.

Mechanics Multiple Choice Exams - same ones I posted in December

Answers to the Final:

 

1-10: BACAEDBECE

11-14: CCCA

15-16: DD

17-25: CDEADECDB

Multiple Choice Mock AP Tests

 

Topic List from the Whole Year

Important and Useful Facts for between April 30 and May 2:

 

Attachment 1 - see it, quick key to today's simple inductor circuit grade

Attachment 2 - see it, very thorough resolution to circuit review things I brought up, not sure how much of this review a person needs.

 

And I said that the following are quiz topic candidates for Wed. May 2: "Anything from Unit VIII and time constants in circuits." Since I said time constants, that could mean R/L, RC, or oscillations involving L and C.

 

Look for me to post more Mock AP multiple choice exams very soon.

Good recovery from quite a few people. This is in my opinion (which is irrelevant as far as the physics goes.)

 

How come: Because to do well on the graded thing of 4/26, you had to clearly express the B of a standard solenoid. A number of people who couldn't do that 9 days ago when it was due the first time have now made it common knowledge. Knowing the field of a standard solenoid is not the B-all and Nnd-all, but it is important, and it's why I think it's good recovery for those who adjusted from 9 days ago and know about it now. (And more importantly, knowing how it applies to things like today's question.)

 

The answer was 3.1 milliHenries

 

Significance: my standard solenoids have an L on the order of milliHenries. To get time-dependent inductance-related changes with them, we'd have to consider the value of L/R for these inductors in a circuit with resistance R. L/R is the typical time it takes for big changes in signals to happen. If this time is too low, we'll never notice the change. Well, an L of a few milliHenries is very low. So to get a time that's greater than a second, an R lower than 3 milliOhms would have to be used. Is it possible to get such a low R when my standard solenoid is wired to power? (Hint: how many Ohms are in the 540 turns of wire of the solenoid already?)

 

My conclusion: I can't create a great enough time constant to see current changes with the naked eye when using my lab inductors. Any ideas of how to change this? (This isn't a practice question. I myself do not know how.)

I've posted some circuit practice throughout the weekend.

 

Quiz of 4/30 will involve the following applications:

 

Using the loop rule in a circuit scenario that could have inductor, resistor, and/or capacitor.

Using the junction rule in a circuit scenario that could have inductor, resistor, and/or capacitor.

 

This isn't news. And lots of practice in the workbook in Units V and VIII and in the attachments to this posting. These attachments have been here for a couple days, with the exception of the Diagnosis one I posted on Sunday 4/29.

 

The LC Circuit Analysis note set attached to this will be of limited value, because it has no junctions in the circuit presented. But the LR Notes do have a junction and are high-level practice.

 

Sunday posting: The document (with the word Diagnosis in its title) is a careful diagnosis of the quality of awareness a person has of the main idea described below. FINAL UPDATE: The Diagnosis document has two Diagnostic problems in it, as of 5:50 PM. And it's now complete. You now have more than enough material, because the workbook is thorough on this stuff as well. And I've long since posted workbook Unit VIII solutions.

 

Main ideas:

 

(If someone thinks the list below is too abstract or symbolic and can't visualize it, then don't use it. Everything that's important to stress is in both my and McGehee's practice documents. I'm just naming the big priorities below. I've used symbols as they were on the board, but maybe they don't translate well in this clumsy Edlio format. No matter, the practice docs are good.)

 

Main idea of circuit section of the class of 4/26: to recognize what the voltage forms are. These are RI, (1/C)Q, L(dI/dt). And to recognize the charge forms. These are Q, C*Voltage, the integral off Idt. And to recognize the current forms. These are dQ/dt, I, Voltage/R, the integral of (dI/dt)dt, which means the integral of (Voltage/L)dt. But big deal. The question is do you know what to do with these forms in something like expressing the loop rule. Do you know what to do with these forms in expressing the junction rule. That's why there were setup tasks on the board, where, given a circuit, you were supposed to value writing expressions like "Voltage1 = L(dI/dt) + RI"

 

And anyone who thinks that's a memorized thing has no idea what I'm talking about. The lesson strongly stressed the skill of going from a diagram to making a unique expression in the format of the one above in quotes. Such a unique expression is customized to whatever circuit diagram is being examined, so this is a communication skill that is being stressed NOT KNOWLEDGE OF FORMULAS. Anyone who doesn't know precisely what I'm talking about needs to get up to speed by using the practice applications and posted solutions notes.

 

Exercise: Figure out what circuit should be drawn if one claims that the following two loop expressions are true for it.

 

Voltage1 = L(dI3/dt) + R1I1 + Q1/C1

Voltage1 = R1I1 + R2I2 + Q2/C2 + Q1C1

I1 = I2 + I3

 

If a person doesn't decipher these three to draw a circuit that corresponds fundamentally to the three expressions, then that person doesn't understand what math usage in circuitry is for. Writing math will only hurt such a person.

Furthermore, realize that a meaningful solution-writer should have no trouble changing one of the two equations above (you figure out which) into something like:

 

Voltage1 = [Resistor1 Voltage] + R2I2 + Q2/C2 + [First capacitor voltage]

 

Equation-writing flexibility is what I'm talking about. Those who don't have such flexibility turn the simplest 10-second solutions into a half hour of formula-driven complication, time-wasting, and wrongness. If this little message is failing to show you what flexibility is, then don't trust it. Use my good word documents or McGehee's. And diagnose yourself with those tools.

 

People who speak fundamental circuit language never say, "Oh, I can't do capacitors." That's a copout statement from one who hasn't practiced and doesn't know that Kirchhoff's Laws are universal and apply to all circuit elements, so no circuit element is "the difficult one".

The Three Quizzes of 4/26, 4/30 and 5/2:

 

2 of 3 will count. If you want them all to count, I can easily do that. I'll give some indication of topic areas ahead of time. Like now:

 

The one on 4/26 will certainly relate to the algebraic form of using Faraday's Law. (You've already been graded on the directional part.) Really, anything from Unit VIII is fair game, but I'll stay away from circuits that have junctions. You could be asked to calculate an inductance, to know how to relate an inductance to a voltage in a simple (junction-free) circuit. Any application of delta-flux over delta-time equaling voltage. Anything from Unit VIII is fair game, so don't think a list here in this message is going to be full; I'm just throwing out some examples. How about Motional EMF; there's another one. McGehee doesn't use the phrase "Motional EMF", but it's a phrase you should know. He DESCRIBES IT but doesn't name it "Motional EMF" on Pages 4 and 5 of the workbook. You should re-review my document on Motional EMF. It's still posted from last week. There is a reason that voltage equals BHv, but what does that mean, and what is H, and why are there two algebraic ways to understand where "Motional EMF = BvH" comes from? See my document for that. Also, Unit VIII Problem 3 is a nice little Motional EMF problem. It uses a lower-case L instead of H.

 

Unit VIII problems - Great preparation for 4/26, but not the circuits that involve junctions or the circuit problems that use calculus. And once you've tried any problem, and really honestly feel stuck, you can peak at the thorough solutions, which are attached HERE!.

 

BIG SYMBOL CONFUSION WORRY: The workbook's symbol for EMF: I don't like it. It looks too much like E field. EMF is voltage, and E field is not; E field has different units. We need to clarify this. See my very brief attachment to clarify this. It's catastrophic if you get mislead by the workbook's bad EMF symbol so quickly read my attachment.

 

Meanwhile, I'll give hints on the topics of the 4/30 and 5/2 quizzes later. (4/30 will certainly involve circuits with some calculus usage and could involve capacitors, resistors, and inductors.)

 

I've also posted "What You Need to Take Away from the Lesson of Tuesday 4/24." Look for this. It's important for measuring how caught up you are.

What You Need to Take Away from the Lesson of Tuesday 4/24:

 

Inductance and its effects in a simple inductor circuit: The circuit that had a 12-volt power supply powering a 4-ohm resistor in series with one tiny circle of wire had a starting current of zero but the starting SLOPE of current was 1.2 hundred million Amps per second.

 

Moving on from this, you were to have learned that value of dI/dt was proportional to the voltage across the inductor. If the voltage across the inductor went down (to say 60% of what it had been), then the value of dI/dt also goes down to 60% of its prior value. The constant of proportionality that links voltage across the inductor to dI/dt is called INDUCTANCE. You were to have learned that today. For the numbers of the last paragraph, you could easily divide the voltage by the dI/dt. Do so now.

 

From the ratio that you just got, you found out that the inductance of the tiny circle was only 0.0000000987 Henry, or pretty much 10^-7 Henry. This is a very low inductance. A low inductance means a very large dI/dt. It would appear to a common observer that such a low inductance would yield effectively infinite slope of I at the instant the power is turned on. BUT if you remove that little loop of wire and replace it in the circuit with a coil with greater inductance, that would lower the starting slope of I, and it would be evident that the current ramps up less instantaneously at the instant when power is turned on. Thus, inductance (and therefore Faraday's/Lenz's Law) slows down changes in a circuit. This was a major idea taught on Tuesday 4/24.

 

I therefore said repeat the circuit problem above, but have it be one of my solenoids in series with the 4-ohm resistor, still powered by 12 Volts. I said find what the new value of dI/dt is going to be when the circuit contains a much greater inductance than the first example. My solenoid has 540 loops, a cross-sectional diameter of 4 cm, and a height of 15 cm. From this, find dI/dt at the instant when 12 V are across my solenoid. That's what you are to have been working on. If you haven't done so yet, try again before you keep reading, because I'm about to give some of it away...

 

 

You're back here, because you already tried the inductance calculation of my solenoids, and you're here to check your answer. You're now supposed to know that you relate dI/dt to voltage across an inductor through:

 

Voltage = L(dI/dt)

 

When L was 10^-7 Henry (the little loop example), and Voltage was 12 V, dI/dt was 1.2 hundred million Amps per second. Now, for this real solenoid, L will be much much greater, Voltage will still be 12 V, so dI/dt will be much much less. That was the main idea. So how do you get L of my coil from the fact it has 540 wrappings, its 15 cm tall, and has a cross-sectional diameter of 4 cm?? Big question...

 

THAT detail (if you couldn't figure it out for yourself) was handled on the handed-out set of notes I provided. It was two pages. I'm expecting you to work through it if you didn't get the L of a solenoid on your own. When done correctly, you'll find that the L of my solenoids is 3.07 milliHenry. But don't take my word for it. Learn to prove it. (And the notes mention another imaginary solenoid whose number of turns and height and area are different. That one has an L of 3.8 milliHenry.) From the logic of these notes, you can also prove to yourself that the L of the very first example (the little loop one) was 0.0000000987 Henry. All three of these Henry values is nothing but a combination of geometric factors, and that was stressed in class as well. Don't memorize. Learn how to derive such L's. That's what my set of handed-out notes was for. It's also re-attached to this message. "Origin of Inductance" is the file name.

 

From this, you could proportionally conclude that MY solenoid hooked up in the circuit above would yield a starting slope dI/dt of 3,910 A/s. This slope is far less than before, because the inductance is far greater than before. A greater inductance makes the circuit slower to change. But 3,910 A/s is still a relatively steep slope so my inductors are a relatively low number of Henries.

 

Measure how well you picked up these main ideas from the lesson of 4/24/18. Apply them to the other quick example I just attached. I call it Intro Example 2. It's quick and useful.

 

In a slight subject change, I mentioned how problems like Unit VIII, #4, are valuable in so many ways. So I handed out an enhancement/discussion/solution hints page I did for #4. I think it's a great review problem of BOTH E&M and Mechanics. And it's relevant to physical stunts recently done in class. My enhancement ends up concluding that for the dropped object to reach a terminal velocity in our presence, the B field has to be around 0.13 Tesla. Check out how I reached this conclusion. It's in my notes but not McGehee's solution. (However, McGehee's solution to #4, which you now have, is useful too.)

 

Even though I handed out the Problem 4 enhancement notes in class, they are also attached to this posting. It's called the Grand Review Problem.

 

So two of three attachments here were handed out in class. Also, they mention dates of "April 29" and "May 1" on them. Just ignore that. Those dates were relevant to some prior school year.

 

One more idea - put an inductor into a circuit on PhET. Use this to visualize dI/dt. I just did so, and that's how I came up with Intro Example 2.

Important Answer Attached:

 

- To the circuit problem set up as the lesson at 9:40 AM on Friday 4/20/18. It was the introduction to Inductance lesson, and it involved the idea of a very tiny circle encircling magnetic field flux when a circuit's current is first turned on.

 

Definition of being caught up as of 4/22/18: a student doing everything s/he can to be good at Pages 1 through 18 of Unit VIII right now. A person would find that this attachment connects Pages 1-15 to Pages 16-18.

Unit VII Lab Experiments (which lead to Unit VIII)

 

The ability to observe these correctly by 4/16 without needing a key was a Unit VII assignment. That's why these documents weren't given out before now. They contain certain answers. The actual conducting of the observations didn't happen until 4/18, and these are now graded.

 

Each person was assigned only two for credit on 4/18. It's presumed that a person who wants to learn with all available resources will do all eight scenarios for him/herself and then creatively make up others as well. I don't have written out documents for all eight of the scenarios from 4/18. I can only do so much, and a studying student shouldn't want me to do all of them anyway. Some have to be left for a student to test him/herself.

 

And now it's learned that Lenz's Law is how to check to see if one is right.

Unit VIII Workbook

 

Do as much as you're ready for from Pages 1 through 15. On Page 16 begins a part named "Self-Induction".

 

On Wednesday, April 18, you'll be doing many observations and recording some of them and handing them in in an effort to reveal something called Lenz's Law. The observations you hand in will be directional. To get these directions correct for credit, you don't have to have prior knowledge of Lenz's Law or Unit VIII.

 

To get these directions correct for credit, you do have to have to have prior knowledge of Unit VII. And that's what was due on Monday, April 16.

 

In addition to what's described above, I'll check some other Unit VI/VII homework knowledge for credit as well. (I was ready to do that on Monday, but I didn't get to it.)

Attachment makes it so someone can see current meters on April 18 and know which direction current is flowing. Required skill.

Due April 16, Monday:

 

Full understanding of Units VI and VII of the McGehee workbook - meaning active filling in of the blanks and written solutions of the end-of-unit problems. (And not written for me. Problem solutions written by you, for YOU, to gauge your understanding.)

The units are already posted (I did so days ago) so people may do them as soon as they like.

 

Do NOT wait to fully understand Circuits Unit V to begin filling in Units VI and VII in order to meet the April 16 deadline. Many people will understand Units VI and VII before they have mastered circuits, and that is fine.

 

The only Unit V fact that it's necessary to know before doing Units VI And VII is the definition of current: in other words, that current, I, is a measurement of how many Coulombs pass a given point in a wire in 1 second. (Technically, I didn't just define current in general but its specific metric unit, the Ampere. Current's dimensions are any unit of charge divided by any unit of time.)

 

So in order to meet the deadline above, you don't have to devote home time to Unit V. But as for Units VI and VII, DO whatever is necessary to budget your time to achieve what I set above as due by April 16. This will likely mean time spent at home working through the workbook. I'm telling you two weeks in advance, so you can space it out even if you do take time off during the break (which I hope you do!)

 

What will happen in class on April 8 and 12:

Circuitry will continue for half the period each day. Tools to measure your proficiency will be available in the classroom. We'll still have time to get good at circuits, because they appear again in Unit VIII, which I will begin on April 18.

 

The other half of the classes on April 8 and 12 will be devoted to classroom teaching on Units VI and VII. It will support what is going on at home as you complete the workbook on these units to meet the April 16 deadline.

Solutions!

 

Some good questions came on Thurs. 4/12. People who asked them were given pushes in the right direction (Unit VI, Problem 10 for example) but I didn't do the algebra for them.

 

I'm thinking that those people revisited their problem, carried it forward and now want a full written solution to compare to what they did.

 

The purpose of these solution documents is to look at them only after you have tried everything you can on any solution.

 

The intention of recent classes was to provide space and time for as many Unit VI and VII facts to get explored as possible. Solving perfection wasn't the goal, because I knew I'd be posting some supporting documents. I said "flesh out the details of this torque setup at home." I still intend to post a couple of those final fleshed-out details. (It's already done in Unit VI, but I like to do it myself as well.) I said, "Move on to Unit VII" and I meant it so that we could optimize the Period 4 class time by getting to the Unit VII demos. That doesn't mean I'm going to leave Unit VI detail problems unsupported.

 

APPLYING THE TORQUE IDEA! This is where it gets fun. Do Unit VI, Problem 15 to see how well you get the main idea. DON'T look at the solution to 15 in the Unit VI Problem Solutions. Don't let that bias you. See what YOU would do on your own with FBD, Newton's Laws, etc. Read #15 and try it solo. Then use my document called "Unit VI HW Help - #15 Specific."

High Level Ampere's Law Discussion:

 

Both files relate to the magnetic field that exists INSIDE a current-carrying wire.

 

 

Completely unrelated to this, I said to know the details of what determines the magnetic field in the interior of an ideal solenoid and to know it by Monday 4/16. Such knowledge would NOT be considered a High Level Ampere's Law Discussion. Despite the solenoid dependence's simplicity, I have yet to have a class of students who all follow this simple instruction to know the solenoid's field dependency by the deadlin. It's not hard to know. Many people do as instructed and know it well. (They simply read for meaning, look at the diagram, and learn the PHYSICAL meaning of every term in the expression. Others vaguely look at the formula, superficially learn the symbols, don't read about it, and know nothing, even though they think they have a formula memorized.) Also, I said the solenoid function is fully knowable whether or not you understand all of the Ampere's Law proof that leads to the function. I said do whatever it takes to know the function.

Repeating what I said in class: In Unit VII, do not let difficulty with the math of the Biot Savart Law section (Pages 1 through 6) prevent you from finishing the SECOND HALF of Unit VII (Pages 7 through 13). The second half is easier. I said if you get stuck on the Biot Savart Law, skip it in the workbook and move right onto Ampere's Law.

 

In other words, have all of the Ampere's Law things well studied no matter what. That's Pages 7 through 13.

 

I also made it clear that it's very important for people to know all the facts about the field due to an ideal solenoid, inside the solenoid. I pointed out that the Biot Savart Law is not necessary for this, and Ampere's Law should be used to derive it. But I also said, "I don't care how you do it; know the final result."

 

That's for Monday 4/16. Moving past 4/16, yes you will need to know how to structure such derivations yourself. By adhering to my 4/16 deadline, you will be a step closer to meeting that higher challenge.

 

Also note: I fully intend to do some Biot Savart math in class. The real deadline for being good at applying the Biot Savart Law is the day of the final, Friday May 4. No credit would be withheld on Monday April 16 for someone being bad at the Biot Savart Law. But understanding of the other parts of Unit VII, as I've indicated and through Page 13, is due 4/16. This final paragraph is just elaboration of things I stated in class.

Not an assignment: Just a summary of a torque analysis that was done on the board in class on Thursday April 12. With neat writing and two diagrams.

 

This is a second way of showing why torque equals magnetic dipole moment cross B field. It's also well done in workbook Unit VI. In fact, maybe this isn't a second way at all; maybe it ends up just like the workbook. My purpose here is just to have on paper what I had on the board in class, which came from an organic discussion.

 

A good application of the result of this concept is Problem 15 from the end of Unit VI, and I posted a thorough breakdown of that problem as well. I posted that days ago.

 

What's due by April 9: knowledge of this post and knowledge of the "Due April 16" post that is nearby this one.

 

Magnetism Units Attached are attached to this post. Units VI and VII.

 

 

At the conclusion of the last test, everyone was given specific documentation saying "Hey, at least 18 of 23 points of this was predictable." I didn't do that for myself. I did it to make people realize that such predictability of material is always provided and will happen again in the Magnetism Units VI, VII.

 

The "Due April 16" posting says when Units VI and VII are due, in addition to some other info.

 

Semester final exam is Friday May 4. It covers Units I through VIII of Electricity and Magnetism.

 

Unit V Resources:

 

1) The fake experiment packet just handed in on 3/28. There's an item in it that turns out to be a place where it's easy to tell who's reading - where I tell people to write down their guess of something. (But I didn't write the question for the purpose of checking up on people.) This guess was important in the learning process. 9 of 20 people wrote down that guess as instructed, so I know those 9 are reading the thing, so those 9 get theirs graded first. Why does this matter? Because an assignment is either your chance to monitor a thinking process or it's numbers to fill in for points. If it's the latter, the learning is weakened. If a person doesn't read the content, then it can't be the former. If it's the former, then a person's engaged in a process, and they can make it their own, and future analyses blossom.

 

2) A resistor-only practice application was in class on 3/28. It's presentation and solution discussion summary (the loop rules of which did happen in class) is attached as the document "Fundamental Family Three Problem Solution".

 

3) Here attached is a neat little set of solving notes called Req Breakdown. But you have to know what Series and Parallel mean before you use it. Here's a fun fact: The Req shortcut for resistors in series is the one you use for capacitors in parallel. And the one you use for resistors in parallel is the one you use for capacitors in series. There is a very simple fundamental way to know why this is so. Do you want to know it? You can ask me during lab time.

 

4) I made "Learning About Equivalent Resistance Series" and "Learning About Equivalent Resistance Parallel" to link the introduction of these connection methods to the animations in PhET. They are animated ways of illustrating the proofs that are in the textbook. Using both of these documents should be extremely fast, and then you go right onto Req Breakdown one after them. Use the Series one before the Parallel one.

18 of 23 points on this were direct repeats of practice. The enclosed charge analyses in relation to flux would not be part of those 18. Those 5 would be the actual measure of your independent thought when you study (and there were practice items that covered that concept as well.)

HW5 Check Solution:

 

Here is the history of this graded item. (Being posted here because on 3/26 I just entered a mix of A's and F's on an item (HW5) that I designed to be nice simple points for everyone to earn, and I gave all the tools to do so with every intention of registering many earned A's for students. I had no desire to enter grades of F for students on this, but that happened for some, and I think that happened for some, because they did not follow directions and didn't do what I assigned. But don't take my word for it. Examine the evidence being referenced below.)

 

I told the entire class on Thursday 3/22 to finish their test with enough time to look at the board and know what they had to do for Unit IV Circuit HW. And I had a clearly written application on the board where I pointed. And I said, "No matter what happens in class today, completion of Unit IV Capacitors in Circuits, is due on March 26." This was written loud and clear in green.

 

I then proceeded to teach that problem at 9:40 or so on 3/22 to many people who were following what I did at the board.

 

I then said that if someone was missing that problem presentation because they were still looking at their the test, I would compensate by posting the same problem online and that I would also post a big comprehensive document called "Ceq Breakdown" (and I made a 1986 hip-hop festival joke.)

 

I then promptly posted a repeat of the board problem (with a thorough set of concise solving notes), and I posted Ceq Breakdown, and I included information about how one document leads to the other.

 

Both of these documents AND the McGehee Unit IV that I said was due provide a nice clean solving method of a certain kind of circuit. And if I hadn't posted my two documents, the material could still be graspable from McGehee's work alone. And there is a textbook.

 

Between 3/22 and 3/26, nobody came to me with any physics problems on this, saying that the above goal was unattainable. The goal was clearly set, as described above, and it contained problems to solve, with answers, so a student could self-monitor his/her understanding.

 

Then on 3/26, a class period ensued. Some circuitry on the next topic was taught. Over half an hour was spent in the library with student self-paced work time at computers. During this time between 8 and 9:40 AM, there were opportunities for a student to let me know that he/she had questions on the items that I said were due for understanding by 3/26.

 

Somewhere between 9:40 and 9:45, I handed out a paper for students to complete to earn credit on the HW goal described above. The paper contained the two absolute most simple versions of the content that I assigned as due. It was far easier than anything on Ceq breakdown or my problem from the board. (It contained a pure series combo and a pure parallel combo of capacitors.) The design here was to have an opportunity for a person to get simple credit for showing some basic knowledge that proved they moved forward in the workbook in the way I said to. People who did that were to earn a strong score, as a part of the effort portion of the class, certainly nothing lower than an 80%. Well, people did that, and good for them, it's what they're supposed to do.

 

But other people didn't. They ignored my effort to help them help themselves, they clearly had no awareness of the definitions being referred to on the graded paper, and another simple problem became impossible to them. I can only assume that this is because they didn't read what I made for them, because if they had, they had over an hour to tell me that those resources weren't working for them. This is why I'm saying that neglect and/or lack of communication on the part of these people is the reason for a grade-lowering experience that in no way whatsoever was my design or expectation.

 

Anyway, the key to this graded item is attached.

Exp. 5 due Wed 3/28 upon arrival, according to instructions attached that were already also given out in class.

 

Circuit Workbook Materials:

 

Electronic Version of Virtual Experiment - Experiment 5: This has an appendix in it that you don't have in the hard copy. The appendix is to help in case you think something is going wrong with the simulator.

 

Unit V of the E&M Workbook. Just motor through the entire unit ASAP. Complete it before you go into spring break. Otherwise, you'll lose a lot of time in stopping and restarting.

 

The circuit file for Exp. 5 on PhET if you want to try to load it. (But you can't just open it. Your computer won't have an application that can open it. You have to download it to your computer, and then attempt to LOAD it from within the PhET environment. But this is purely optional. You can also make the circuit yourself.)

Due Monday: Full completion of Unit IV so that you could solve for the charges on any capacitor in a multi-capacitor circuit.

 

I've attached three supplements to make you invincible at this skill:

 

1) "Introduction to Capacitor Network Solving": I did an example problem at 9:40 on Thursday 3/22. That example is repeated here and then a bridge is built from that example to the useful idea called Equivalent Capacitance. People not hearing me solve the example problem (for whatever reason) especially need to access this document. That was at least 10 people on Thursday 3/22.

 

2) Ceq Breakdown - Do this after "Introduction to Capacitor Network Solving".

 

3) "Introduction to the True Definition of Series and Parallel" - this can be looked at any time before, during, or after the above two documents.

 

Keep in mind that the goal due Monday would be doable using McGehee's workbook alone. My supplements are intended to make it better.

 

To get to the circuit simulator, go here:

 

 

Note: At 5:50 PM on 3/23, I found I had to make a small correction to a page reference in Ceq Breakdown. The document had said that it parallels Pages 9 through 16 of McGehee's Unit IV. That was true for an older version of the workbook. The pages are now 7 through 12 of Unit IV. I have corrected the Ceq document, and the corrected version has been attached here since 5:52 PM on 3/23.

Midterm on Thursday 3/22. Note: an enormous cushion has been built into the training for this midterm. The midterm's not covering anything that wasn't mentioned in class by Friday May 16. It's entirely inappropriate to be absent for this midterm on March 22. Any invalid absences will not be given make-ups. I want to avoid giving any make-up tests. A valid absence would create a situation of taking the test later in time. Tests taken later in time are more challenging and cover more material, which would be fair because the student has had more time to use the workbook and the textbook to learn more. I strongly recommend against it, because it's harder for me and the student. Be present on the scheduled test day. I expect that people will. (Note: a person who has already discussed a March 22 absence with me before now is fine. It's a rare situation, and this person took care to give me advanced notice, and I appreciate that.)

 

In addition, I already gave away a capacitance task that will be done for credit on the midterm of 3/22. (I said it twice in class, Friday and Tuesday.) Anyone paying attention is supposed to take advantage of that and score those points with little difficulty. Such a give-away of a task for points would only be done on the 3/22 test and not on any conceivable make-ups.

 

Important Items for the remainder of a person's midterm studying, in descending order of importance:

 

1) The Capacitance Lecture (AKA Comparison) Problem Document Solutions - From what I said to do in class on 3/20, you're supposed to be asking for this key. It's attached, along with the original. A particular capacitance calculation is a large part of the midterm, as mentioned above.

 

2) A reminder of something that some people pretend doesn't exist unless they're told to pull it out. I don't do things that way. If I gave it to you, it was important, and it was important two weeks ago - "Gauss's Law Mastery Practice". Do you still have it? Did you do it over the last two weeks when it would have been most effective. (For certain people, the answer to that is yes - I've seen their work on it, and they're getting good at this stuff.) The wealth of key versions I just attached for this represent all the questions that could be asked about this very useful document.

 

 

5) Unit II Problem Solutions - I hadn't posted these yet. I had posted Units I and III solutions. The author tells you to do problems as you work through his notes; you're supposed to be asking me for answers to end-of-unit problems. Obviously, the more you make these a steady diet, the stronger your lasting comprehension. Have you looked at McGehee's nicely written solutions in these solution documents?

 

6) Caught-up people at this point can be going to the College Board site above and taking any year and doing the electrostatics problem (usually the first one) as a mock test, writing the solution, with a strict time limit. You then go to Scoring Guidelines, and you grade how you did. This is a gift, is it not?

People in class were told to do at least through Page 6 of Unit IV, and that much is on the midterm, and they were given the Unit IV hardcopy in order to do so. Unit IV is attached.

 

Attached is the full set of answers to two practice scenarios that were on the board on Wed. 3/14.

 

The scenarios involved this skill: predicting the way that V and E vary with spatial coordinate near charged sources. Many examples are possible. The two in question on 3/14 were conductor sphere and thick insulator slab (AKA thick plane). I didn't specify the charge well on the sphere problem, and that was a mistake, so it was a dirty example but the spirit of the underlying concepts was communicated. In case that's a problem, this attached version is very clean with zero ambiguity and all answers available for checking. These only have answers, because other documents discuss methods and solution steps to many more problems like these two.

 

Other documents are more thorough on these types of problem. The Boot Camp one was handed out last week. A 6-page solution discussion of the Boot Camp one is now attached here. (The attachment also contains the original practice questions on the first page of six.)

 

The two board problems in 3/14's class were there to communicate the kinds of things you should be practicing and what that practice should look like, as communicated by things like the Boot Camp document.

 

Also, I here attach one more example of how the Experiment 3 analysis goes and how you can check your conclusion. Should be useful.

Unit III Text: You're not responsible for doing any part of this by 3/8/18.

 

It's always good to go as much forward as you can in the workbook when you have time to do so - work ahead.

 

The things I did say to focus on, by talking in person and in another nearby internet posting, can be helped by this Unit III workbook, but they can also be done without it.

 

The most important of things going on right now, as mentioned in another post, between 3/6 and 3/8 is the Concentric Circle graphite paper data set that the whole class recorded on 3/6.

Experiment 3 - Assigned individually to each of your in this attached document. I think it's thorough. Bring your knowledge of this into Monday's class on 3/12, and be ready to use the Period well, focusing on this assignment.

 

Your name is in a chart on this document. What you do for credit depends on your knowledge of numbers assigned to you in the chart.

 

The document contains specific directions on what to do if you pair up with somebody, so read it.

 

Here I attach 2-page document that includes an answer to the main exercise that's in the document called Circular Symmetry in 2D (a file you can see in another nearby post.) This attachment has the main math help that should help you to understand what to do in Experiment 3.

Answer to HW that was due on 3/6/18 is 2,403.6 Volts.

 

See me personally for help if you either got it wrong or didn't do the problem for any reason. I did not post notes on this problem's solution, nor will I have time to. But the setup of it was thoroughly shown in class.

The Most Useful Thing to Do between 3/6 and 3/8 is attached here.

 

This is what I called in class the biggest bang for the buck problem to solve. It falls right from the voltmeter data that I had the entire class recorded while Ryan Bloodgood and I measured. It is a great data set.

 

Do the graphing puzzle that's on this 2-page attachment, and you will learn a lot.

 

This will move your knowledge greatly before the quarter midterm. It is also the foundation of Experiment 3, which is the most important experiment of Quarter 3. For more information on the midterm and labwork dates, there will be a posting with some calendar dates. Keep an eye out for that.

Key to the little reading check I did on 2/26 - Attached

 

This was a good aid for you to check your comprehension. If you got them wrong, it had value. If you got them right, it had value. No matter how I grade it, see this value. I'm happy with whatever you did on this as long as you read the key and think about it.

 

Do my cylinder notes before 2/28, Part 1 at least. Quality over quantity. When you're feeling the quality, you move to do Part 2. Part 1 is required as HW. Part 2 is: "now I'm working ahead, and I'm totally going to because Part 1 gave me momentum." Being unable to work ahead on Part 2 doesn't lead to anything bad.

 

These two cylinder note-sets, mentioned as Part 1 and Part 2 above, are attached for anyone who was absent.

Homework due Mon. 2/26:

 

You have to know some specific E field facts from Unit II as described below. If you don't like the Unit II workbook, you can get these facts from the textbook as well. The specific facts were communicated in class, but I'll elaborate here as well:

 

The content is covered in McGehee's Workbook, Unit II, Pages 1 through 12. The more detail you can get into on those pages the better. But however that goes, know the following facts by the 26th:

 

E field caused by a very long rod, as a function of distance from the rod.  It's not just a matter of reciting a formula and saying the word "lambda" in that formula. You have to know physically what lambda refers to. And you have to know what its units are. Lambda is a kind of density.

 

E field caused by a very large-area two-dimensional plane of charge. It's not just a matter of reciting a formula and saying the word "sigma" in that formula. You have to know physically what sigma refers to. And you have to know what its units are. Sigma is a kind of density.

 

Absolutely know lambda's and sigma's units by February 26, and know them forever after.

 

So you see there are two functions you have to memorize, but it's more than just memorizing, as described above.

 

Furthermore, in the E field formulas referred to above, in places where distance factors in, you have to know precisely what segment in space is being referred to. And if distance does NOT factor in, you especially have to know that important fact.

 

The page 10 resolution of the field due to any disk is a somewhat ugly formula to memorize. But it gets nice and simple when you let the disk's radius approach infinity. Definitely focus on the result in the infinite-radius limit.

 

And then you may wonder, "how can you have a finite charge Q if the radius of the disk is infinite?" Well, do the workbook: you'll find out that that's why the field answers are written explicitly in terms of densities like sigma instead of in terms of a charge symbol.

 

Unit II of the Workbook - big attachment here - as of 2/23, no one has come to me for a hard copy, so that means each individual is comfortable printing out their own at home. Or at least the first 12 pages of Unit II

 

OK, this post is fully updated now. I won't be adding to it throughout the weekend before 2/26.

The homework due on February 26 depends on you understanding today's superposition quiz, so I said I'd post scanned copies of my succinct solution to that. Attached here.

 

There were four versions. Only the solution for Version 1 attached has a little marking of where the points come from. My rubric points are not written very neatly on that. The rubric is:

 

3 points for name

1 point for sticking to Coulomb's Law with dimsenional consistency

1 point using the right distance in Coulomb's Law

1 point for cancelling out one axis's componenents

1 point for doubling the other axis's components

1 point for properly choosing the trig function multiplier

1 point for a simplified answer magnitude (sine or cosine of anything not allowed in final answer)

1 point for correct direction of final answer stated

Several solutions to E field vector addition practice problems are attached:

 

First one: It's from 2017. It's excellent, thorough, and mirrors the class of 2/20/18.

 

Second one: 2018 document. Written-out full solution to the last E field addition problem I did on the board in class on 2/20/18.

 

Third one: McGehee's Unit I end-of-unit problem solutions. These problems contain at least two superposition examples that a person would use for practice. People are supposed to try them and then be wanting to check their work.

Due Tuesday February 20: Experiment 2 write-up

 

Much similarity to Experiment 1's Write-up, which is graded so get that back and don't repeat any mistakes. (Most did get that back, but there have been a couple of absences.)

 

ERROR ON MY HELPER DOCUMENT!! On the file attached here, "How Not to Screw Up Exp 2", there was an error in the accounting for the q and the Q in the advice on how to do Problem F. I gave you the hard copy of this file in class on 2/15, and that contains the error. The hard copy's paper title is "Write-Up Standards Repeated for Experiment 2 of Semester 2", but the file name is "How Not to Screw Up Exp 2" for those who downloaded it electronically before. Either way, if you got the file before 3 PM on 2/15/18, your copy contains the error. The one attached to this message now does not contain the error.

 

Reason for and nature of the error: If you look at the Unit I Problems of the Workbook, in #8 you'll see this same oscillator problem, and in that version, Q is the name of the moving charge and q is the name of the stationary ones. The "error" I'm talking about in my helper document is a formulation of the potential energy calculation that assumes the charges were named this way. Because of the existence of #8, this alternative formulation was still sitting in my document as a relic of the past. But I've done away with that, so the new version, attached here, is written under the assumption that q is moving and Q's are stationary, in order to match the standard way the class has been naming them. If you have any confusion, just use the new version, attached here, if you need help on Part F.

 

And I'm now including an explicitly done U calculation, attached here now, in case my document error has you worried. (It shouldn't because it's been corrected.)

For Experiment Write-up Due Tuesday 2/20, here's a checklist to make sure you're doing it right:

 

Make sure you know your assigned mass, b, and amplitude values and stick to them.

 

Already have chosen a good set of Q and q values that will give a decent period. (Q a power of 10 or two less than q would be good.)

 

Make sure you have measured the oscillation T on the computer (or pretend you have.)

 

Do what's on my assignment sheet, in the form of a scientific write-up, using the helper document "How Not to Screw Up Exp. 2" to help you and realizing that I had to correct an error in that helper document. (See other post that states the due date for Experiment 2.)

 

Since I had that error in the "How Not to Screw Up Exp. 2" document: to undo any damage from that, I've now attached to this message an explicit example of U calculation (Question F from the Experiment 2 assignment) with usage of sample data.

 

Put a lot of thought into how the change in U between release and equilibrium relates to the change of another form of energy. Use this idea to check your work before you hand in your write-up.

 

If you really want to work ahead, what is the Taylor series approximation of the U(x) formula you chose to use in Problem F? (This Taylor series approximation is the thing that makes the SHM form of potential energy close (but not equal!) to the Coulomb's Law form of potential energy that the workbook stresses at the end of Unit I.) Please be clear: you are required to answer Parts F and G with the Coulomb's Law form of potential energy. Again, the explicit example of this is attached.

Experiment 2 Data Spreadsheet

 

See this so you know what to do for the fake charge assignment.

 

FYI: We'll be focusing on potential energy upon release, potential energy when passing through equilibrium, and maximum KE in the motion predicted by SHM theory.

 

Those areas of focus are going to mean that the prediction of period is old news. That's why that's already been graded, grades recorded, and this spreadsheet gives away the key for that predicted period.

 

Note: Have your q be at least a power of 10 greater than Q, maybe even two powers.

Heads-Up: Now in this space are the energy notes that have to do with electrical potential energy. It's something I began in class, and will relate to Experiment 2 in a big way. I began the conversation in class and you'll need to look here to make sure your were getting the reason for the conversation, after you're done with your pendulum write-up. Only the full pendulum write-up is due at 8 AM on 2/13/18.

 

But this energy analysis starts with Unit I of the Big Electricity Workbook. Attached. You may print this at home if you like. But I'm also planning to give you hard copy of Unit I.

 

So what's the connection to Exp. 2? In class, I said do the integral that derives potential energy near point charges. That result is on Pages 21, 22, and 23 of this attached workbook. It is fine to jump to those pages now and work out of order. From what I've said in class, you should have the language needed to read Pages 21, 22, and 23 after never having read Pages 1 through 20. So study those pages to see if you were getting the main idea of what I mentioned in class about potential energy.

 

Next: calculate the system potential energy of your set of three charges in Experiment 2 for the instant t=0.

 

After that: calculate the system potential energy of your set of three charges in Experiment 2 for the instant when q passes the equilibrium point. Calculate this according to the methods of Unit I, Pages 21, 22, and 23 and not according to the methods of simple harmonic motion approximations.

 

For the above energy calculations to not get too unwieldy, I recommend you make charge q be a couple of powers of 10 greater than charge Q.

 

The difference in appearance between energy from first principles (Pages 21, 22, and 23) and the energy shortcuts of SHM methods is the main idea I'm trying to get across in the write-ups for both Experiments 1 and 2. ("But Exp. 1 wasn't electricity", you might say. Yes, that is right, but that one still has a potential energy based on first principles that looks nothing like the SHM shortcuts, and I did make a big deal about that on 2/9/18 at about 9:40 AM. This will all be illustrated in class.

Assignment for the Electrical Oscillation:

 

But before that...if certain people (66.7% of the class) don't want to repeat their mistakes on the Electrical Oscillation, they need to read the following...

 

I have written evidence (based on the pendulum write-up) that 13 of 36 people have read the details of what I've put online, and I'm talking about details that clear up any misconceptions about certain graded items.  I'm specifically referring to the precise wording that I put into Item 5 of the posting that's titled "Compound Pendulum - Final Write-up Due 8 AM Tuesday 2/13 - Updates Now Final".

 

And I'll repeat that Item 5 here in quotes, with emphasis added to what I already wrote by making it bold:

"5) Everything to the right of Column Z is where I will program formulas to grade the rest of your write-up. It should be helpful to look at what's there. I put a gift at the very far right for everyone. Note: when I ask you to determine a kinetic energy, you have to calculate it by direct means. You may not assume that it matches the loss in U and just report that as answer. But definitely use the loss in U as a comparative value for what you calculate for K. This helps you check things and then say Physics!!! after you fix any errors you catch."

 

So if I wrote Did not Follow Directions (DnFD) on your Pendulum write-up, I'm referring to this, and by writing "DnFD" on your paper, I'm stating that you have done the exact thing I said not to do. Furthermore, the thing I said TO DO is still written right under the clock where I put it on 2/9/18 at about 9:40 AM when I said it. So the information was delivered in person and in writing.

 

Once again, if people read what I give them and/or listen to what I tell them, they'll save themselves a lot of trouble. Instead, there are people who choose to go by rumor from what some other student tells them, and it's often wrong and a waste of time. If 13 of 36 people are using the verbal and written facts I give, that tells you that working from what you've heard from other students has a high probability of being uniformed. There are absolutely people who know precisely what is going on. And their habit is to do internal comparisons in their own work. They go by physics principles (energy conservation, for example) and find comparisons useful for their own error checking. There were quite a few outstanding Experiment 1 write-ups.

 

A previously attached document called "Rotational Energy Intelligence" was super explicit about this math that I keep saying I wrote under the clock. So the help is coming verbally and in writing.

 

Electrical Oscillation: All mistakes like that described above will be repeated by individuals who don't access necessary information on their own. Classmates are not the source of that information. The assignment sheet's attached. I've already discussed (and posted online) how you use the McGehee workbook to get the facts, and you can decide whether to do things the factual way or the rumor-based way.

 

You may perform the analysis of the Electrical Oscillation for now as if your theoretical period is identical to your measured period. (They basically will be, because it is Interactive Physics.) Everyone who did it got their graded period calculation back for the electrical oscillation, so those people are well-supported.

 

Note: The "How Not to Screw Up Exp 2" attachment here has been corrected as of 3:30 PM on 2/15/18.

Compound Pendulum - Final Write-up Due 8 AM Tuesday 2/13 - Updates Now Final

 

Resources to help have received their last update at 9:34 PM Saturday 2/10.

The resources are the following:

 

Spreadsheet attached: Deluxe Version attached here. You can do the whole write-up on your own, but here's how to use the spreadsheet, and I think it's helpful:

 

1) It has all the data that I knew for everyone. Anything data-related has already been graded. If anyone thinks I have data recorded wrong, they can tell me. If a person can't find his/her ideal predicted T values in Column V and W, then he/she can fill any missing data into the data columns (to the left of the Danube River), and then perform a formula-drag on any columns where things are calculated to the right of the Danube River.

 

2) For data sets that are sufficient, ideal predicted values of T will sit in either column V, W, or both. One or the other is fine. If you have good predictions in both columns V and W, you may pick which to use. Both are good for me, and you've already been graded on that ability to do the predictions represented by V and W. (And it was possible to get 10/10 on that prediction even if both V and W cells are empty in the current attachment.)

 

3) Column Y - it would be a true prediction if all rulers were center-of-mass balanced right on their 50 cm marks. It's based on a theoretical weighted average calculation of d. Column Y's answer assumes a symmetry that I don't think is true so I don't think Column Y is official. But I put it there for your information. It's interesting that it gives a lot of people a very good agreement with the measured T.

 

4) I'll assume that you make the rest of your write-up, (according to my directions and to what's in "How to Not Screw Up the Pendulum Write-up"), consistent with Columns B and either V or W. If you instead base the write-up on Column B and Column Y, please make that clear immediately in the write-up. You are the scientist; you can decide, but you have to communicate. Also, if you stick with V or W, please pick one or the other and not both.

 

5) Everything to the right of Column Z is where I will program formulas to grade the rest of your write-up. It should be helpful to look at what's there. I put a gift at the very far right for everyone. Note: when I ask you to determine a kinetic energy, you have to calculate it by direct means. You may not assume that it matches the loss in U and just report that as answer. But definitely use the loss in U as a comparative value for what you calculate for K. This helps you check things and then say Physics!!! after you fix any errors you catch.

 

5A) The column to the right of Z that is called "Coeff" is referring to the coefficient that you're supposed to put in the standard form of the 2nd Order Differential Equation. I'll be grading the numerical value of that strictly with units exactly as "How to Not Screw Up the Pendulum Write-up" instructs. The document also says why entities like that appear twice in the grading spreadsheet.

 

6) If your name is not Ewald, Galvin, Irish, or Lach, don't read their rows. I put some instructions for them in Column K in hopes that they too can use this spreadsheet.

 

7) To be clear, I already graded the prediction of T, so it is perfectly fine for anyone to borrow my formulas that are in this spreadsheet if they did anything wrong up until now.

 

Everything to the left of Column Z is what I used to grade your 10-point assignment that was due on Wed 2/7 and that everyone got back. (Except for Mikael Purne, who did his well but I failed to give it to him - Mikael, I'll find you Monday, and either way, you and all students can see your data written nicely in the spreadsheet attached here, so I think everyone still can know how they did.)

 

That's it for the spreadsheet.

 

Other attachments in case they help:

 

Electronic copy of the full write-up assignment sheet I gave out in class.

 

Electronic copy of the broken down discussion of doing the write-up well. This is called "How Not to Screw up Pendulum Write-up". This document was also given as hard copy in class. I said a couple of those things about doing it in a high quality way in class on 2/9/17. Much of what I said on 2/9 had to do with calculating energy in a meaningful and way and having one's eyes open to a way of checking energy.

 

A two-page summary of what I said in class about calculating the Rotational Energy Intelligently.

 

Note: People who didn't earn 10 of 10 on both parts of what's been graded so far in the Compound Pendulum should make full use of the spreadsheet to avoid repetition of mistakes.

 

With the support I've given, I'm expecting high quality write-ups that I'll correct quickly. Anyone who disagrees with that as the expectation would come and see me Monday 2/12, the day before this write-up is due.

Exp.2 Simulator

BIG help with HW due Friday 2/9! Attached!

 

The attachment will help you confirm what you did in the algebra to get F = -(Const)x.

 

The document will confirm what you should have gotten for Const.

 

As I said in class: Your HW job: using the knowledge of Const., figure out what your values of Q and q could be to give you a reasonable value of period T. For reasonable, let's say anywhere from 5 to 100 seconds.

 

Rule: Q can't equal q.

 

If you never wrote down your assigned parameters for A, b, and Mass, they are reposted here as well.

 

More advice: If you know Const., omega squared follows the usual laws of SHM. In other words, omega squared equals Const./m, where m is mass. From that, you relate period to the product of the charges. Then you pick your charges to give you a T you like.

Due at 8 AM Wed 2/7: something related to this notice. Nothing new, already announced but read this.

 

What's due Wed. will be called Exp1 - just the predicted T part, not the full write-up.

 

What I'm entering now is credit for data handed in last week. About this grade for Reporting Accurate Pendulum Data - of the first 8 data sets that I attempted to enter, only 4 will earn credit. Why? Well, any of the following occurred in the 4 rejected papers, and I'm only 8 papers in:

 

- Changing the meaning of symbols from what I clearly depicted in instructions and then giving no diagram to explain the new symbol meaning that the student intends. As if the reader is psychic. I could handle new symbols if the reporter diagrammed them.

 

- Basic illegibility, a length marked with a symbol, and the reader can't tell what symbol is written.

 

- Writing something like "Q = 0.501 m". As if I'm supposed to know what you mean as a distance. "Q=0.501 m" marks a distance, you say? Distance from where? I spent time in in the instructions to clearly depict that Q is a point in space and is not a distance. I don't know what you intend me to visualize as the distance from some unspecified other point to that Q position. That's why my instructions clearly define a distance from hole to point Q as something called "D". Someone who adhered to my directions and reported a value of D would be adhering to what the reader said he needed. Students who write "Q = # m " as data: You're imprecise and unclear and won't get full credit, and you're expected to put yourself in the reader's shoes. These aren't rules because some teacher wants to be controlling: the reader has no way of knowing whether you meant Q's distance from the hole or Q's distance from the end of the stick, and by not thinking of that it means you didn't visualize, which means you didn't do physics. And there is no way the reader/grader can validate any credit. I can't make up values to insert for missing info. The reader isn't psychic.

 

Because I put time into being careful about distinctions like those above, and used diagrams and words to do it, I'm not spending time to decipher the impossible-to-follow reporting from data reporters who refuse to pay attention to detail in the way that I did. So credit can't be awarded to things careless in this way, and it's physically impossible to correct even if I wanted to award credit.

 

Keep this in mind as you prepare to report your theoretical predicted period, which is due upon arrival on Wednesday, 2/7.

 

If anyone sees a poor grade in something called CW1, it's certainly because of the type of carelessness described above.

 

Of the first 8 that I have done so far, the following were clear data sets: easy to enter and validate, not rejected. They'll earn either 100% on the CW1 grade or some kind of A, depending on their percent difference: Colomer, Crump, Dupas, Smith

 

In the comparison between theoretical T and measured T, I'm going with 100% on CW1 for data sets that yield 2% error or less. Some kind of A for 5% and lower. There's a reason why the idealizations for pendula are reliable and not marred by friction and why low percent errors are expected. There's a physics reason. See if you can think of it.

If you have a laptop you use for school, bring it on Wed. 2/7/18, especially if it has a disc player.

Predicted Period of the Compound Pendulum, solved on paper, is due 8 AM Wed. 2/7/18. This was stated in class on 2/5/18, and no individual raised an objection, so it will be graded for accuracy right away on 2/7. This is true for people who have been absent as well as present. This material is not news, and 2/7 was originally the due date for the whole write-up. Whole write-up is now due 2/9.

 

People were also told to be consistent with the data sheets that have already been given to me. I'm still in possession of those. Anyone who needed to see those data sheets had a chance to do so on Monday, so it's expected that every individual is/has completed the prediction of the period from his/her own data. I specifically checked to make sure that all students had copies of their own data in their possession.

 

Notes attached here summarize the compound pendulum period calculation. (This will be the fourth time this solution has been shown - twice in class, once in the document called "How to Not Screw up the Pendulum Write-Up", and now attached here.)

 

I am going to make an effort to complete the recording of the class data set into my spreadsheet by tonight. When I get it all entered, I will post what I have here, and maybe by Tuesday night. (This is going slower than it's supposed to go, because not everyone follows directions or puts themselves in the shoes of their lab reader. No reader should have to work hard to interpret a data section, especially in this case, when I've defined symbols with care.) Again, the posting of this spreadsheet has nothing to do with a student's ability to do the calculation that's due on Wed, as explained above.

 

All of this says that my correction of this predicted T on Wednesday will be a discussion-free, immediate thing, and students will either get it right for good credit or the bad alternative (which I hope doesn't happen, because the way I see it, there's no reason for that to happen.) This is all extremely well-supported and I've highlighted the evidence that validates that claim.

Contest Results! Look at this spreadsheet. Lowest value in Column O is the winner.

 

We'll have a similar one for the Compound Pendulum.

 

Thank you SO much for measuring the Compound Pendulum in my absence on 1/30/18. I think it's impressive to perform a good experiment under the conditions of this week. Once again, Andrew Xie deserves a HUGE amount of credit in pendulum assembly. Now your job is to hand in clear, complete data at 8 AM on Thursday. By following the directions, that should be simple to do. Completeness of data has been defined in the instruction sheet. (The papers I gave you had diagrams in at least two places so nothing is ambiguous.)

 

If you've tried but are incomplete with the theoretical predictions for the Compound Pendulum, that's perfectly fine. Theoretical predictions in the Compound Pendulum are not due at 8 AM. But it's good at this point to try to complete the rest of the SHM packet.

 

On Thursday, February 1, I will finally grade the homework that was due last Thursday that I haven't collected yet, so be good at anything on the first 6 pages of the SHM packet, including plugging a function into a differential equation. This last skill is stressed on Page 2, 2A, and 2B of the packet.

 

So I'm grading two things on Feb. 1: The data that are due for the Compound Pendulum AND the SHM Packet Pages 1-6 HW that was due on Thursday 1/25.

 

Side note: those of you who like math. Look at the graph tab in the attached spreadsheet. You'll see a graph that shows the value of x that gave the maximum omega-90. Could you derive this maximum theoretically by taking a derivative and setting it equal to zero?