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Studying Self studying please help

  1. Mar 8, 2013 #1
    I have been out of school for over a year now. The reason for this is that I was bored with the classes I was taking at the community college (calc 2, physics 2 and physics 3) to the point that I could not concentrate on earning A's, among other issues, not quite sure why given that I had gotten A's the previous year without even paying attention or studying or doing the homework. In the past year I have been studying on my own, which I find works far better than listening to a lecture, which for me makes me too tired to concentrate on the book and stores memories of the material through episodic memory, which is a most inefficient way to learn, and, I believe, results in learning difficulties analogous to memory based trauma.

    Anyway, I found that I understand things better if treated at a higher level. The particular classes I was taking were mainly about memorizing things that would be far more efficient to teach while studying harder subjects (come to think of it I don't know why calc 1 and 3 aren't taught concurrently since learning how to do it in three dimensions isn't really teaching anything new, unless I am much mistaken about the content of the curriculum or if it is just unusual that I can think in that way) and I found that, for example, reading a third year level book on electromagnetics made a lot more sense than the lower division treatment. Would anyone suggest, say, an upper division to graduate level book that treats the topics covered in physics 3 (waves, optics, modern physics) at a high enough level to actually understand well enough to remember without rote?

    A while ago I bought a book titled "Mathematics of Classical and Quantum Physics" (Byron & Fuller) and only recently have I felt confident enough with my math skills to open it. I find so far that I understand everything and can remember it well, I've been reading it for about a week and I'm on the third chapter. Is that good progress? Bear in mind I have to read it on days that I am not going anywhere or doing anyhing so that I can fully concentrate, and although I have absorbed everything from each chapter before moving on to the next one I have not worked out the problems yet, I shall after I have read all the chapters but I prefer to let the material ferment in my head for a while before I attempt any problems.

    What other books should I be reading? I want to study physics and chemistry and math and I am trying to save up money to take the GREs and or take graduate level classes at UCSD via extension (I am not allowed to apply for admission until I get 60 credits, that's what I get for being talked into starting at a comm. college although it seems to me the four year setup would work far better for me) and in the fall maybe go back to the comm. college and take classes in everything EXCEPT the math and science classes - I don't trust myself to get good grades in classes that require you to memorize the dumbed down way and test you on the lectures that are poisonous for me to listen to.
    As for replies, if its not a problem, I would prefer responses to be PM because the moderators here like to move my threads to different forums and then give me infractions when my replies go a little off topic (which is rubbish because any good physics discussion is going to cross disciplines) I would like advice and suggested readings and perhaps what kinds of things I can do to be impressive enough to transfer to a private school or get a full scholarship to an out of state school. I have considered switching majors on paper (because my credentials as an artist and a writer are far more impressive than my credentials so far to be a physicist) and then transferring and switching back as soon as acceptance is locked (I see no point in even minoring in a subject that I have done a good enough job of mastering on my own, and that does not strictly require a degree to work in anyway) and working on the professors to let me take higher level classes.

    Some other things to know:
    -I have an incredibly long memory. I don't forget. Ever. Not even math that I never use.
    -I can only concentrate on one thing at a time. Hence, if I have to go to class on a certain day, I can choose to either forget that class or forget about studying for the day. All attempts I have made to multitask in the least bit have failed.
    -I have a hard time controlling what to focus on. If my mind decides it wants to be stuck on something else, I can forget about doing what needs to be done for the day.
    -I am a 23 year old female who was not allowed to go to college until 2 years after high school, and who was not allowed to study college level physics and math until I was freed from my controlling foster/adoptive parent (sorry I really hate making these excuses but I am not lazy just so you know)
    -I take 5 mg of Adderall a day. That is a small dose but if I were to take any higher I would probably get a panic attack. It helps my mood and my determination and confidence more than my attention; as a matter of fact, it may be making it worse, by making my thoughts more hyperactive; people see how fast I talk and how hyper I am and they think I am anxious or manic but I have always been like that, and my experiences with calm down pills have been awfully demotivating...
     
  2. jcsd
  3. Mar 8, 2013 #2
    You don't feel confident in getting A's in classes you perceive to be about memorization but also claim to basically have a photographic memory?
     
  4. Mar 8, 2013 #3
    A very selective near-photographic memory, and I am almost completely out of control as to what is selected.
     
  5. Mar 8, 2013 #4

    jim hardy

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    I'd say start working the problems. That'll force you to 'take charge' and direct your concious where you want it. "Where the concious goes the subconcious must follow."

    When you find something that interests you you'll focus on that.
    Best programmer i ever knew was a physics major who worked in missile tracking systems at Cape Canaveral. He branched out into industrial process control...

    Pick up a book on Modern Control Systems. It's pure math applied to real things, and there's need for that talent in this day and age. At worst you'll be bored for an hour.
    We used Dorf's first edition when i went through school. It's up to 12 now.
    https://www.amazon.com/Modern-Control-Systems-12th-Richard/dp/0136024580
     
    Last edited by a moderator: May 6, 2017
  6. Mar 8, 2013 #5
    Yes I do need to learn some programming, I need a live person to help me with that though. I took a free programming course on edx from Harvard and I got bored right away, because of the childish computer program called 'Scratch' they decided to use. I just signed up for the MIT edx course but the python enthought wouldn't download properly.

    I find that true, when I am working on problems my focus is better. It doesn't stick though unless the knowledge of how to solve them is firmly in my long term memory, otherwise it will all go into disposable short term memory. My short term memory is terrible. My working memory works really well drawing on long term memories but not short term memories. For me long term memory equates understanding it. I basically run through the problems in my head as I read through the book, as they show you how to do them, check to make sure the math is right, pick up the new procedures being introduced, and later try to run the sequences in my head without looking, and solve some problems in my head before solving on paper. I hate having to use a pencil and paper and a calculator; it breaks my concentration to get the calculator out and the pencil and paper make me want to doodle. I actually got very good at doing math in my head because of this!
     
    Last edited by a moderator: May 6, 2017
  7. Mar 8, 2013 #6

    fluidistic

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    Hi CosmicKitten,
    From reading this thread I get the (maybe wrong) feeling that you believe that math and physics courses are meant to be memorized or read+memorized and as soon as they enter in your long term memory then you have learned the subject.
    To me, "learning a course" is being able to solve any problem thrown at you. Sometimes I don't know the order of the chapters and I might have jumped 10 pages of a chapter but as long as I can solve the problems in the end of the chapters I'm confident I know what's going on.
    You talked about a 3rd year book on EM. I don't really "read" these books. Many times I have to get a pencil and a paper under my hands to derive the formula that are presented. This is the only way one knows where and how they come from. I personally don't feel like I'm reading a book, I feel like I'm just doing an exercise or solving problems.
    For example there: http://www.phy.duke.edu/~rgb/Class/phy319/phy319/node59.html, boundary conditions on a conductor. Do you know why ##(\vec D - \vec D _c ) \cdot \hat n = \sigma##? (eq.10.1 or you can even take 10.2).
    I know where they come from and how to derive them. If I only read them and read that they come from "inserting eq. xx into eq. yx" I wouldn't consider I really know the material given in the course. For higher than freshman level courses, reading a physics book like a novel is not going to work. In fact I would even say the same for freshman book like Halliday and Resnick Fundamentals of Physics. Solving the problems is to me the utterly most important part of the course and this is what determine whether I know the course. I'm sure I'm not alone thinking in a similar way.

    I might have got a wrong impression of you though and you might study efficiently.
    Also I would like to state that the freshman level EM course is not really a watered down version of the higher level EM course when it comes to the physics involved. Mathematically of course they are totally different but the physics, i.e. calculating the potential, electric and magnetic fields is essentially the same. At least for the electro-magnetostatics part.

    All in all, I personally believe that being able to pass calculus 1 to 3 (i.e. solve the problem thrown at you) is very important. If you can't do that, I find it hard to believe you can understand what's going on in a upper level EM book although you might memorize what you've read from A to Z.

    One more thing, calc. 3 should not be taught at the same time as calc.1 or 2. since it involves vectors, Jacobians (hence determinants which belongs to linear algebra), line integrals and other linear algebra related maths. So unless you're taking a linear algebra as well as calc.1 and 2, calculus 3 would not make much sense. Bear in mind that this is my opinion based on my own experience.

    I wish you the best of luck with your studies. Don't be afraid of pencils, try hard not to doodle them. If you know how to solve the exercise because you've thought on the problem already then you should not doodle at all.
     
  8. Mar 8, 2013 #7

    jim hardy

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    i understand.

    Creative people ofeten have trouble concentrating. I think it's because they're so bright and ordinary school comes so easy they never have to learn to concentrate and focus. They get good grades without ever learning to exert.

    Maybe one should think of that 'gift' of mental agility as somewhat of an impediment ,
    in that it keeps us from developing to our potential,
    and recall the story of Demosthenes:
    http://itotd.com/articles/319/demosthenes-stones/
    By your own statement you have avoided the exertion of working problems.

    ANECDOTE - i hope it doesn't bore you...

    Here's how i got started programming. It was before the IBM PC .
    We had a sociopath in management who took delight in torturing people.
    Monthly expense accounts were his favorite tool. He'd find a tiny yet obvious addition error, strike a diagonal line across the whole page with a magic marker and return it. That meant you had to re-transcribe the entire thing, and re-check every addition. I'm mildly asperger's and often swap digits or mis-key the calculator... so it was a problem for me.
    It took a couple hours to rewrite and double check a form. Pure mean spiritedness on his part, he even looked like Mr Potter from "It's A Wonderful Life"(Lionel Barrymore)..

    I shared your disdain for rote transcription and menial arithmetic.
    And i had a TI-99 home computer. And a printer.
    So i brought the computer to my office and wrote a Basic program which prompted me for expense-able items day by day. It stored them on a 5 inch floppy disk.
    On demand, it printed them in the exact same format as on the company expense account. And it did all the arithmetic. So i knew there were no addition errors.
    Now all i had to do was transcribe to the company form. Also i knew that any mistake was an error of omission not an error of addition... i'd simply missed an entry.

    I added one more feature to the program - with one keystroke i could adjust every entry for which no receipt was required up or down by 1%. You see, i knew darn well he knew where any mistake was. By changing everything i made HIM repeat HIS tedious checking of my arithmetic.
    AND i could have the new form back to him in ten minutes. Ha Ha Ha Ha Ha Ha! i deprived him of his pleasure.


    Well it worked. After three cycles he started sending my forms back with a sticky-note indicating the problem, instead of a magic-marker swipe.

    And I learned how to handle input, strings, arrays, formatted print, Ascii special characters and disk I/O in Basic.
    END ANECDOTE ----------------

    Moral of THAT story - We need motivation. We learn by doing.

    So quit making excuses and get to work making something that you can look at a year from now and say "I did that well! ".
    Even if it's only this with every supplementary problem worked:
    https://www.amazon.com/Schaums-Outline-Feedback-Control-Systems/dp/0071635122


    !
     
    Last edited by a moderator: May 6, 2017
  9. Mar 8, 2013 #8
    Oh, yes it does in fact appear you are quite mistaken. When I said that long term memorization equates understanding... What I meant was, I dunno if understanding it puts it in my long term memory, or if having it in my long term memory causes me to somehow understand it better, but I know that for me the two go hand in hand. I mean, if its been in my head for a whole, I can more easily apply it. You might say my memory works better the longer ago, rather opposite to that of most peoples; the knowledge does not rot but rather ferments. That is my impression anyway.

    I tend to understand concepts very quick, too quick as a matter of fact so I become bored and although I have a basic understanding of the material I don't remember all the finer details of the equations as well. This is ironic because I tend to remember equations and constants better than most people.

    Anyway, in my calc 2 class anyway, what they taught was techniques for finding out whether a series converges or diverges, and also L'Hopitals rule, and basically how to solve improper integrals. I could not find a list anywhere of improper integrals tables, you know for the trigonometric functions, the tables on Wikipedia were a load of redundant formulae and none of the ones I needed, I sought tutoring and although I understood everything well enough to interrupt the teacher before they were done explaining, I could not effectively remember any of it. Why? Because spoken word and any activity involving social interaction for me just doesn't encode in an easily retrievable mode. I should have asked for a piece of paper with all the formulas to memorize -- I can figure out my own explanations better than the teacher can explain them, that way it won't be by rote - or gotten a book that explains everything well enough, but I couldn't find one and was probably too stressed to search effectively. At the same time I was studying differential equations on my own, and I apparently understood them well because I got to thinking about the n-body problem and discovered that it could be approximated in a way using power series - my only problem area in calc 1 - and that was before I read later in the book and found out this was called the Euler method.

    Also, I find compulsory homework to be problematic. It puts you in the wrong state of mind - rush it and get credit instead of learn it - and takes away time from working on your own problem areas.

    Linear algebra is easy - I am a very visual thinker, so matrices make sense to me. Learning about the angular momentum tensor helped me to understand them better.

    And the third year electromagnetics book cleared up curl and divergence and gradient for me. These were not taught in the time I was in that physics 2 class, I think they should be taught very first thing. Apparently they can't be taught at that level because they require knowledge of calc 3? You know what, they should just load up the students on math and hold off physics classes until they can teach them in more mathematical depth. Also, the textbooks and class notes (purposely perhaps?) left out a lot and I guess you had to pick up that knowledge from the teacher? Which is too bad because as I mentioned earlier I have a deficit in oral comprehension. So I try to tune it out to avoid distracting episodic memories but then I see stuff on the test I KNOW I didnt see in the class notes. Either that or I couldnt concentrate (I was not medicated at the time not that that's any excuse) or I suddenly have test anxiety and I have NEVER had test anxiety before. I in fact scored 34 on yhe ACT, 35 in math, and in my previous physics classes I got the highest or second highest score on most of the tests, suffering only labwise (I dont work well with others, provided I can even get others to be my lab partners)

    As I read this book, I find myself rather impatient with some sections, and at times jumping to understanding things before they are even revealed.
     
  10. Mar 8, 2013 #9

    ZapperZ

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    I find this hard to believe.

    One just doesn't "read" such a text as if it were a novel. I lost count how many times I hear students telling me that they understood the material when they read the text, but found it difficult to solve the homework assignments. To paraphrase Mary Boas's message from her book, you only get a superficial understanding of the material by simply reading books or hearing lectures. The only way to have a deeper understanding of the material is to solve various problems, and to practice this often. From what I've read, you seem to have an aversion to doing that.

    Secondly, you are not a very good judge on whether you have mastered or understood the material. You may claim that you have understood "everything", but how do you prove such a thing? I've read books on performing surgery and I believe I've understood everything. Piece of cake! Shall I take out your appendix?

    Zz.
     
  11. Mar 8, 2013 #10
    I tried Schaums before. I found them very not ADHD friendly. Maybe different now that I'm medicated...

    That's why I have to study harder problems. Is it odd that I can carry out most of the entire Euler Lagrange equation in my head but not memorize that other stuff?

    As for programming... Not sure I quite got that story, nor would I find swapping keys like that funny unless it were a prank played on that particular individual that I HAAAAAATE (not going to say who she is or she will probably try to get me arrested again for 'slandering' her... But she probably doesn't frequent this site anyway.) And yeah I'm mildly Aspergers too.

    I did a bit of programming on a graphing calculator for a calc 1 class (in high school, but a small one with no AP tests, idiot bastards made me take it again in college instead of letting me test for credit out of it, you can only pass out of as high as precalc which some engineering majors had to retake and they were fresh out of high school too having taken calc 1 AND calc 2 while in high school, how pathetic, I would NEVER hire them to design a bridge, no wonder that towns infrastructure was shot... Can't blame them though, the high school class was garbagety. Spent the entire first quarter reviewing trigonometry, barely covered integrals by the end of the year, and that teacher, like the one in college, was a condescending louse. I studied ahead in the book as much as possible, but I was also very depressed so I don't think that studying was very effective. )

    I somehow got away with checking out a book on nuclear physics a book on vector calculus, and a book on molecular spectroscopy while I was 19 and still under control of the abusive person I mentioned. I had no internet, nothing to distract me except a television I seldom watched, so I studied all day and wrote stuff down that made no sense later and in two or three weeks I picked up most of calc 3, linear algebra, a bit of ODEs, and a bit of quantum mechanics. And then I was told to take the books back and pick up something at the library 'worth reading'... like Twilight. But when I got back to studying a couple years later I remembered it all surprisingly clearly.
     
    Last edited by a moderator: May 6, 2017
  12. Mar 8, 2013 #11
    I do not have an aversion to doing problems, I just prefer not to do them until I feel that I fully understand everything. Plus, this book does not even have answers to the problems to make sure you know how to do them.

    That I believe is part of the problem with many lower division classes. They make you do problems for credit, which takes away from your study time so you don't know quite how to solve the problem but you're in a rush to get it done so you do three quarters of the problems and get half of them wrong but still get full credit. And then get a failing grade on the test but if its a high F you can still pass from the homework and attendance credit (this is more typical of c.c.'s than four years or so I am led to believe).

    All I know is that this book seems so much clearer to me than the other, easier books I have read. I certainly don't read it like a novel; if I did I would have finished it in one or two days. I look at the problems as they go step by step and sort of make up my own rules on how they work (and by making up I mean most of the time ripping off whoever discovered how to do it that way but it sticks better if I feel like I'm making it up haha) and I check all of the work from step to step (THIS is how I learned much of what I know about calc 2 and 3) and if I don't get why that step follows I agonize over it until I do and this can sometimes be distracting or cut a marathon study session to a screeching halt, so I attempt to take back the reins by searching on the internet...

    And then there are times I get Eureka moments that I enjoy a little too much (like today I was all "aaaahhh I discovered how m by n matrices relate to what they discussed about isomorphic vector spaces I have an even better idea now of what matrices are all about!") Which are certainly encouraging but also distracting...
     
  13. Mar 9, 2013 #12

    jim hardy

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    Soounds like maybe you've had a time of it.

    The science books you read are above my level. So i cant address your original question.

    Your difficulty in slowing down to focus is all too familiar... i addressed that in myself with myriad self-help books... now that was in interesting journey!

    This may sound strange, but i found a lot of comfort in reading Jodeph Conrad's "Tales of the Sea", a colllection of his short stories. Every one is a character study. I gained insight into my own strengths, weaknesses and behaviors from it. Sorta helped calm the storms, if you will.
    Good luck and hang in there .

    old jim
     
  14. Mar 9, 2013 #13
    No, not odd at all. You have a normal memory. You remember some stuff, and not the other stuff.

    But I am not quite sure what "carrying out most of the entire Euler Lagrange equation" means.
     
  15. Mar 9, 2013 #14

    WannabeNewton

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    Who cares about memorization in the context of physics and math problems? Why the constant memory rhetoric? It doesn't matter if you can memorize the Euler Lagrange equations in your head (one can easily look those things up); this is a useless trait and you focusing so much on it only takes away from you focusing on traits that actually matter when it comes to solving physics and math problems. I think in order to get any proper advice, there has to be a shift away from all this prolonged memorization chatter and go on to how one can properly absorb concepts and subtleties and subsequently apply them to proofs and physics problems. These kinds of things come with practice not memorization.
     
  16. Mar 9, 2013 #15

    micromass

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    That's exactly the problem, isn't it? You can't understand anything unless you do the problems. It's not like reading a text again and again makes you understand it. You can only understand if you do the problems. If you didn't do problems yet, then you don't have a full understanding of the topic. You'll have superficial understanding at best.

    And books which have answers are really unnecessary. You should be able to do problems and know that you did them correctly.

    So you just "make up rules"?? That sounds like a recipe for disaster. How do you know your rules are valid in general? How do you know when to use which rule? Why do the rules even work?? It sounds to me that you're just memorizing a book without actually learning the material very deeply. And making up rules is a very bad thing (unless you can prove the rules to be true).
     
  17. Mar 10, 2013 #16
    Hey, I'm not the one who thinks memorization is all that important, it's the schools, or at least the schools I went to. I can understand the process and the meaning behind it completely, and then get a D on the test because I didn't remember the formula in perfect detail. Same goes with almost everything I self taught, given just a few reminders of the formulas and stuff I can solve just about everything but since you are usually not allowed to have access to such details on an exam that makes me sad knowing I wouldn't be able to ace the exam unless I do.

    Of course, if you truly understand the formula, then the details and everything else follow naturally. But elementary level textbooks don't contain the full derivations and explanations required to understand the formula well enough to memorize it without rote. If a calculus formula was derived using partial differential equations or even higher level math, then that should be taught before one is required to memorize it, unless they are to be pigeonholed into a career that doesn't require much understanding or thinking, as I imagine is the goal for most community colleges and the insidious 'cooling out' process that they carry out, am I correct in that assumption?

    I went to a four year college for one semester (I left and went back to a community college because I had to move and the latter was the only option available to me where I moved, and the four year college, having no physics majors, was not worth staying at anyway) and the classes were not in fact taught at a higher level. As a matter of fact, I found the physics 1 class very easy, because I was not required to do homework for a grade, I only had to worry about the tests (its too much of a strain on my attention span to have to worry about homework for a grade every night plus I get too tired in the head from sitting through lectures to concentrate) and I got the highest or second highest grade in the class on nearly all of them, without doing the homework or studying (not that I didnt try, but I simply couldn't concentrate, especially with all the other things I was worries about at that time of my life). I was able to figure out problems I had never done before in the time given to take the test. Plus the teacher never covered most of what he should have covered; it was mostly stuff I remembered from high school, and I had a similarly easy time in that class as well. Electromagnetics and optics are a little less intuitive however, especially regarding laws that require a higher level of math than is taught to fully understand the rules, and thus rote memorization, or a higher level book to supplement the class (provided you have time after the homework which I try to do during lecture since I am too tired to do by the end of lecture) is required.
    In short, I had a hard time in comm. college because I WOULDN'T memorize by rote. Not sure if wouldn't or couldn't actually, perhaps a little of both... I wasn't failing, I mean a high D on the tests can be brought up to a B with homework and attendance and labs, but that to me was unacceptable. I'm still not sure how I could do so poorly... And yes I studied and got tutoring too. It was always the case in math in high school that I got A's without understanding anything because I almost rotely memorized the rules. Luckily I was able to look back on it later, when I wasn't forced to do homework, and find that I could suddenly understand everything at a level I didn't while I was in the class. Most people I think would forget it altogether?
     
  18. Mar 10, 2013 #17
    By making up rules, I mean I figure out my own process for doing them, because I have a hard time paying attention through the steps given sometimes, or a hard time memorizing them. I can't even articulate what goes on in my head most of the time, I am very visual and I try to visualize what they are describing, and I check all the units if they are using units to make sure they provide the desired thing that is to be measured, whether it be meters, meters squared, meters per second times mass (momentum), momentum times distance which is the same as energy times time (units of Planck's constant or 'action') since these can be treated as pseudo-variables that can be canceled out or raised to a power. This aids understanding and memorization, and is a problem area for most students if I am not mistaken? What is the main problem area for most students anyway?

    I will in fact spend a little too much time focused on things like that. Even if the problem is clearly laid out I feel like I am missing something if I don't see how all those work at first. Sometimes I see right away, and forget...
     
  19. Mar 10, 2013 #18
    This sounds like you are making many excuses. You should probably take a step back and realize that these grades imply you do not understand the material as well as you believe and also understand that you do not need partial differential equations to have a very solid grasp on intro physics.
     
  20. Mar 10, 2013 #19
    I think I was in fact overthinking. Instead of listening to the teacher and picking up on the 'dialect', so to speak, of that particular class, I just observed the class notes and old test questions, did the homework problems (which did in fact include the answers so you would think I would know what I needed to work on?), and looked in the book, having thought that everything I needed to know was there, or apparently not knowing what I needed to know. If they would only put everything on one big sheet of paper and let you have at it *sigh*

    First question on a test I scored 41 on from Fall 2011 Physics 196 (E&M):
    On the x-y plane, the electric field is uniform and is given by E = 400i (N/C) (E and i are vector quantities). Point A has coordinates (-1, 1) and point B has (2,0) if the electric potential at point B is 300V then what is the potential at point A?

    First off, does it even make sense that there is electric potential in a uniform field? Maybe yes but at the time I was used to thinking of electric fields as growing stronger the closer one moves to the source, this kind of electric field is unnatural and impossible to occur in real life and maybe that's what threw me off, I mean if you took the divergence of it you would get zero just like with a magnetic field (they didn't teach divergence in that class, shame it would have solidified a few concepts for me) but anyway if I just took the antiderivative of the electric field and got 400x, 400(2) - 400(-1) = 1200V, this also doesn't make sense, because clearly the voltage cannot equal 300V unless x equals 3/4 which it doesn't but why is this supposed to make sense anyway it's electromagnetical lala land in the fantasy world where an electric field has zero divergence. It should have been a no-brainer to realize that 1200V is just a difference and that it must equal 300V - V_A (V_B - V_A since that's the way I did it) and oh look we get -900V which is not in the answer options. Say we take V_A - V_B: 400(-1) - 400(2) = -1200V, V_A - 300V = -1200V, V_A STILL equals -900V. No clue what I did wrong here...

    Second problem, ok the electric field this time is 3(x^2)i, which does have divergence and I guess it could be from a pair of same charged plates. Antiderivative of 3(x^2) equals (x^3) and the task is to find the potential difference between x=1 and x=3. That would be (3^3) - (1^3) = 27-1 = +26V. But that was marked wrong; maybe it was -26V?

    Problem 3 is... electric potential V(x,y)=2xy-(x^3), so in units of V/m, you must find the electric field at (2,1)... the x derivative of V(x,y) is 2y - 3(x^2), the y derivative is 2x, so the field would be E = (2y-3(x^2))i + (2x)j, to plug in (2,1) into that would get -10i + 4j, which I marked but according to the teacher is the wrong answer.

    And then there are problems I'm not sure whether I got right or wrong because the cat went potty and blurred out the red x or check, and a picture I was required to draw field lines and equipotential surfaces (how does the teacher decide it is worth 2 out of 3 points? No clue...) and although I thoroughly understood capacitors even back then, I screwed up an entire 18 point problem because I... looks like I multiplied the voltage by the area of the plates and divided by the separation distance... ugh I knew even then that you are supposed to multiply area by distance and those other two constants and not bother with voltage for the other capacitance equation that you use when you are given area and distance but not charge, the equation was even written on the cheat sheet the teacher allowed us to make, how did my reasoning lapse so badly? The rest of the work that followed was fine apart from the grossly oversized value of capacitance I got for the first problem... stress, I guess, I even saw something was wrong right before I had to turn it in and so had no time to fix it.

    And here's one problem where I did the integral right but I just forgot to plug a and 0 back in to take the antiderivative from a to 0.

    So like I said I massively screwed up on a couple of things but mostly NOT because of not understanding it well enough, but rather... test anxiety? I am not one to normally get test anxiety either...
     
  21. Mar 10, 2013 #20
    This is not often the case.

    Yes, it does make sense.

    You know that [tex] \nabla\cdot{\bf D} = \rho [/tex] but do you really know what it means? This is not inconsistent with a uniform electric field if one is looking at a region that contains no charge or if there are discontinuities in the boundaries which is often the case with idealized problems.

    Second, suppose a uniform electric field can't exist. One could certainly construct a field that varies very little over space and might be approximated as uniform. A student of physics should be able to appreciate the necessity of approximation.

    But in any event, its moot. You must of seen the scenario that leads to uniform fields.
     
    Last edited: Mar 10, 2013
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