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Do exams really reflect knowledge?

  1. Dec 17, 2015 #1
    Do you guys think exams and problems in physics really reflect your knowledge of the subject? I find myself having superior knowledge of theory in my courses relative to classmates (I often explain it to them), but then I can't reproduce this on exams which are all computation. What do you think?
  2. jcsd
  3. Dec 17, 2015 #2
    Yes. I think, based on so many of your posts over the last few months, you don't understand the material as well as, time and time again, you say you do.

    Since this is in academic advice, I'm going to give you some advice. Read what people here write to you every time you make a post like this instead of ignoring them and constantly trying to fish out responses that'll reassure you of your decisions in life. You clearly don't understand the material if you aren't doing well on exams. You clearly have a poor self image of yourself and are trying to use PhysicsForums to boost your waning self confidence. And all of this is clear to everyone who posts here regularly.

    Take some time this holiday season and seriously consider what it is you want to do in life and how poorly you're going about the task now.
  4. Dec 17, 2015 #3


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    Examination are not a perfect reflection of a student's knowledge or understanding of a subject. They are time-limited, subject to bias, and at best are a random sample of the knowledge base the student has acquired.

    But they're the best means of evaluating students that we have. There may be other options, but those are subject to limitations as well. As you expand in time - say with term projects, essays, or assignments - you lose control over the conditions of the evaluation. You could rely on the students to self-report, but in competitive scenarios such reports will not always be honest, and are likely subject to other biases. At least with an examination, everyone is under the same conditions.

    If you're struggling with a feeling like you know the material, but you just struggle with tests, the good news is that you can always get better at taking tests. Most universities will have resources for students who suffer from exam anxiety. You can attend workshops or read up on exam-taking strategies. You can practice exams. You can identify problem areas for you and develop plans to improve them.
  5. Dec 18, 2015 #4


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    Why don't you speak with your professor and ask them for a chance to explain the material to them?

    I would say one-on-one examinations would give the most accurate picture of a student's knowledge, but
    in very large classrooms, these don't seem feasible.
  6. Dec 18, 2015 #5


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    How would you know that your explanation of the theory is actually correct? After all, this is the "blind leading the blind" case. If, for example, you think you understood Gauss's law, but you failed to use it correctly to solve a problem, then that failure is a clear symptom that you have NOT understood it. We are not looking for a politician here, which is someone who has the flair for the dramatics and can talk him/herself out of a paper bag. Instead, we are looking for someone who can back his/her claim in actually producing something worthwhile, which is when an idea is applied to several situations that create outcomes.

    There are good exams, and there are bad exams. The good exams DO evaluate your mastery of the material, and NOT just mimicry or regurgitating what was covered in class.

  7. Dec 20, 2015 #6
    My experience with several QM courses is the instructors (professors teaching) side with Feynman. Parphrased he said, no one "understands" quantum mechanics, the real test is whether the scientist can calculate (e.g. photoelectric cross-sections, scattering results, wavefunctions, ) with it. Your question seems to indicate that the tests do not test understanding, but moreover, the problems (say on HW) do not test understanding.
    I too was poor at tests (although I slowly got better enough to pass the qualifying exams). The HW (when the course HW as graded) often saved me. Given enough time to settle down, I usually did well. (I once got a B-, and the professor told me I would have failed except my HW grades were better than everyone)

    Your question asks whether a complete understanding of the subject matter is possible without being able to calculate at all with it. My answer is: Not in physics.

    The professionals I know would rather the colleague be completely confused and be able to calculate with the theory than the colleague "understand" it completely and not be able to calculate with it.
  8. Dec 20, 2015 #7


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    It would not be as common in physics. PURE SYMBOLIC FORM was often emphasized in much of the instruction and examinations. The first real Physics course I had, (mostly to learn the calculus-based Mechanics, the first in the sci/math/engineer sequence), solving everything symbolically was most of the needed results expected. Computation accounted for maybe 10 to 15 percent of credit for an item. The professor even once gave an examination in which NO COMPUTATIONS of any kind were asked nor expected; but all problems were to be solved only in variables.
  9. Dec 20, 2015 #8
    I agree with Symbol. My Mechanics course was the same way. We would even get advance problems that were obviously outside of the level of class instruction. The teacher would grade us how we approached and why. Not on correct answers. My instructor for EM freshman physics course was the complete opposite. He graded more on correct answers then actual method. I would be extremely pissed after every quiz ( quiz were every class meeting). I could never remember the values for the constants and would receive partial credit on an answer that was correct. I just needed to plug in the value of the constant and boom right answer. Really hated that guy.
  10. Dec 20, 2015 #9
    I have only had one instructor that made such crappy test and it was not even funny. The teacher would come to class with a hangover ( I have seen him stumbling out of the same bar I was at), was late to class, or just showed up when he felt like it. This was for ODE. He would make an extremely long test and give us 2 hours to finish it, sometimes an extra hour. There was never enough time. It was like he randomly opened the book, picked 16 problems, and slapped a test together in 5 min.

    My other teachers, made test that were a lot better. Solutions manual could not save you. They never chose a problem from the book. They all created test were you would learn something new. Ie. Add an extra layer to the problem, but in order to solve it, you have to have mastered and understood the underlying concepts.

    My favorite problem was in Calculus 1. You know those graphical problems where you need to see how the the derivative of the graph looks, when just a geometric picture is given. Our teacher gave us one complicated graph and he asked to take the 7th derivative of it. Turns we could have stopped after the 3rd derivative. Nothing more happened. Everyone had different answers. He gave us all full credit for that problem and laughed.
  11. Dec 21, 2015 #10
    No test is perfect. You said before you had a 3.5ish GPA. You obviously know something. Maybe you just had a tough round of classes recently, it happens.

    I think solving problems is what really makes a person good at physics though. I know several people who can talk up a storm about all types of advanced theories but can't solve even the most simple problems from freshman mechanics. You need to be able to apply the models you learn to novel (but appropriate) situations.

    It's possible you just had some bad luck recently, who knows. If you want a physics degree just keep working hard. Never allow yourself to feel like you like you know a lot, I try to go out of my way to make myself feel dumb almost all the time. Keeps me pushing hard :).
  12. Dec 21, 2015 #11


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    How does the answer to this question even matter? You don't have a choice but to do school the way it is designed.
  13. Dec 21, 2015 #12
    I think that it does, but also it does not. In general, doing well in an exam means you did understand everything that was tested on it (or most of it at least). But it does not mean you know all of the subject (things that were not on the test you may not know completely).

    Alghtough, getting a bad grade on an exam doesn't mean you don't know anything about the subject. This happens with certain frequency on exams with calculations and problem solving, where you must pay attention to all the details, then, for instance, take someone who didn't sleep well last night, he/she will probably make mistakes they wouldn't if they were completely awake (with a good night of sleep) . And this applies to a stomachache as well. Just because you are feeling bad right on the day of the exam, it doesn't mean you don't know the subject.

    Also, some people get nervous when doing and exam, and that can be very comprimising to their grades.

    To sum up, I think there are many variables to say if an exam does test your knowledges or not. In general ways I think it does, but you can't rely only on them (or entirely on grades) to say if someone has knowledge X or not. I myself have lived such case, where my classmate did better on a test then I did, yet, he did not know some basic stuff of the subject that, for his lucky, were not in the test.
  14. Dec 21, 2015 #13
    Talk about making assumptions and false claims as a "scientist". I actually have quite a high self image . I apologize for posing questions to others in hopes of getting everyone's opinion in order to make a good decision. I'm definitely going to reconsider my life because of your post and I'll reconsider applying to graduate school with my horrendous 3.6 gpa and 4.0 upper level gpa. Thanks for helping out. Happy holidays.
  15. Dec 22, 2015 #14
    Why do people do this? Why do people make threads asking for an opinion, and then get upset when they don't get the opinion they want? Makes no sense...
  16. Dec 22, 2015 #15

    Vanadium 50

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    Because they are looking for validation, not advice.
  17. Dec 22, 2015 #16

    Andy Resnick

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    To be fair to the OP, (I've been watching this thread to see how it develops, feel free to split this off to a new 'person-independent' thread) the design of tests is highly non-trivial because of the central question: "what does this particular test measure?"

    Clearly, different tests measure different things- for example, a multiple choice, closed-notes exam measures different skills as compared to a free-response, open-note exam.

    Personally, I struggle with creating exams for the intro sequence- colleagues call my questions "context-rich questions", and they are open-book/open-note. Here's an example question: " I saw a 10g acorn fall from about 10 m up, hit the sidewalk and bounce back up to 2 m. How much mechanical energy was lost, and where did it go?" My primary goal here, as with all my exam questions, is to measure the student's ability solve problems by first identifying the essential concept(s) and ignoring irrelevant details, and then apply the appropriate equations. Correct computation is worth a minority of points.

    In my experience, only 20% of the class gets anything approaching the correct answer to the above question. The most common error (> 50%) stems from trying to apply kinematics of collisions rather than conservation of energy. The next most common error is the use of inconsistent units- [mgh = (10)(9.8)(2)J]. It doesn't matter if I work a similar problem in class prior to the exam. More generally, nearly all my students seem incapable of "ignoring irrelevant details".

    For the past 6 years I have been teaching the intro physics sequence, I have documented a near-exact zero correlation between homework scores and my exam scores, indicating that homework problems (these are from the book, I don't generate homework questions) are not helpful preparation for my exam questions. More concerning is what I wrote above: working out similar problems in class also apparently does not prepare students for the exam. So I continue to struggle with helping students learn how to solve problems.

    One alternative approach is to simply use 'canned' exams that more closely match homework problems- for example, state problems in such a way that there are no irrelevant details. That's fine, but those exams measure different things than my exams.
    Last edited: Dec 22, 2015
  18. Dec 22, 2015 #17


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    Dr. Resnick,
    Be assured, that although you are frustrated with what you find as a teacher of Physics, your efforts ARE WORKING. I know this, because I was like many of your students. We do improve. The help you give does matter. The way you describe what you do is the way you should be doing. Homework really is beneficial. So many Physics 1\2\3 students have not yet learned to think analytically with the Physics subject yet, especially during the Physics 1 - Mechanics course.
  19. Dec 22, 2015 #18

    Andy Resnick

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    Gosh, now I'm blushing :)

    Seriously, tho- I think PF is a great resource for students, and I mention it in my syllabi.
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