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Testing The Physics GRE, thoughts? Opinions?

  1. Apr 20, 2010 #1


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    So a professor of mine and another student were having a discussion about the PGRE the other day. While it does seem to be of the overall opinion that it is only good for determining how well a student can take the PGRE and not really how good they are at being a physics student, I've come to a different conclusion. I've noticed that the people in my department who can't do physics worth a damn and who should have picked a different major a long time ago are the same ones who can't score beyond 20th percentile even while they're doing their masters degree at the time of taking the test.

    For example, one of these students I posed a question to: If you drop a ball off of a building and simultaneously let another ball roll off a ramp connected to the building at the same height, what would reach the ground first? They couldn't figure it out... and these are people who want to go get their PHD and teach this stuff.

    So most people say you shouldn't judge someone based on how well or poorly they do on the PGRE. My contention is that if you can't do well on it, you have no business trying to get into a PHD program. Your thoughts and opinions?
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  3. Apr 20, 2010 #2
    if thats exactly how you worded the question and some how I bet it was even more vague when you asked it then I can understand why they didn't give you a good answer.
  4. Apr 20, 2010 #3
    I don't know about the physics GRE but the general one I did. The verbal bit seemed to basically be a vocabulary test. It seemed to be more about what you know, rather than how you think.

    Also I hate that you can't go back to answer questions. I think that plays to the advantage of people experienced in this kind of testing, again, not so much in quality of thought.
  5. Apr 20, 2010 #4


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    What is the friction due to air and drag? What is the height of this building, and is there another massive object around the two balls? What kind of material is the ball made of? Is there a wind breeze, or perhaps freezing temperature variations that could affect the friction rates of the ball on the ramp, and what is the deal with airline food?
  6. Apr 20, 2010 #5


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    No, this happened half a year ago, I don't remember exactly how I worded the question but obviously it was not a problem of vagueness. It was your typical idealized point particle frictionless world. Even so, absolutely irrelevant. The fastest path is straight down along the gravitational field regardless of moment of inertia or friction or what have you outside of one object being shielded from the hurricane that was tearing down the building and only one of the objects.
  7. Apr 20, 2010 #6
    would it depend on how slanted it is?
  8. Apr 20, 2010 #7
    I'm no physics student (yet) but whats the answer to that question? Assuming that everything i.e friction is negligible then won't they hit the ground at the same time.
  9. Apr 20, 2010 #8


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    No. The ball travels a longer distance on a slant, and the force of gravity is multiplied by the sine of the angle of the slant, hence the smaller the angle the slower the ball moves. The maximum acceleration due to gravity is achieved at a 90 degree (vertical) angle or simply free fall.

    If the problem was dropping a ball from height and shooting a bullet horizontally from the same height at the same time, in theory the bullet should hit the ground at the same time as the ball because there is no obstruction for the bullet to go downward vertically as is the case with the ball on a ramp.
  10. Apr 20, 2010 #9
    Ah I see, I was thinking of the gun example. I just thought the freefall option was too obvious, got tricked by thinking it was a trick lol.

    Well I have lots to learn when I start physics next fall. Never really cared for the subject back in highschool.
  11. Apr 20, 2010 #10
    Common sense tells me at least two things:
    A) The ramp is like a hypotenuse of a triangle whereas the length straight down is like a side.
    B) Ramps decrease the rate of work being done.

    Anyway, I'm currently in my first semester(Spring 2010) of college, when should I plan to take my GRE? I'm thinking that I will probably take an extra semester or two to graduate because I want to double major, but I'm not sure if that will hamper my chances of getting into a good grad school.
  12. Apr 20, 2010 #11


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    No the question wasn't the bullet out of a gun example you hear so much about. The ball hits the ground first that is dropped straight down.

    Whatever. That isn't the point here, the question is the usefulness of the PGRE and everyones opinion on it.
  13. Apr 21, 2010 #12

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    Note that this doesn't require any knowledge of physics - just observations about what happens with ramps. (And "ramps" that we see every day - we call them "hills") But I agree that someone who has trouble with this idea will have trouble in grad school, and will - or at least should - have trouble with the PGRE.
  14. Apr 21, 2010 #13
    After reading the questions it seems like it is a good measurement of the students physical intuition which while it isn't the be all end all skill to have for a physicist it is certainly extremely handy.

    Some are just awful at it which is why the test is needed, it isn't something you can see from his grades or courses or anything really.
  15. Apr 21, 2010 #14


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    The Physics GRE is most definitely a lot more than a test of intuition. It is a test of your knowledge of the most basic concepts and principles in a number of subfields. If you can't get at least half those questions right, you have not been exposed to enough physics or haven't absorbed enough. You need to spend more time with Physics before getting into Grad School.

    Similarly, I believe that if you can not score over 750/800 in the Quant section of the General GRE, you haven't been absorbing enough math for Grad School.
  16. Apr 21, 2010 #15
    Well, the problem with your argument is that there are people who can do all of the calculations and would be able to answer everything on that test but would do it too slowly to get a good score.

    Of course I would argue that then they don't understand what they have done but that in no way means that they are not able to do well in grad school or in academia in general.
  17. Apr 21, 2010 #16


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    There are a lot of conceptual questions, however, which I like (even though for some reason most the people I know hate the idea...). Other then that, if someone realizes that ETS designed the questions to take less then 2 minutes and they're solving a mechanics problem through say, the entire Hamiltonian formalism, it's a good indicator that they don't have a lot of intuition about the problems.

    For example, a popular question with them seems to be 3 masses connected linearly on a spring all with the same mass, same spring constants. It looks like:


    They give the tough frequency of oscillation and then would ask what is the other oscillation mode? I know a few people, when given that question, derive the whole problem through Lagrangians and small angle approxmations and all that and don't realize, even though they've seen and done the problem before in a class, that you just get your 1-mass frequency when you hold the middle one and let the 2 side masses oscillate by themselves.
  18. Apr 21, 2010 #17
    Unless they've changed the PGRE radically in recent years, this sort of question is not the type of question that the PGRE is focused on.

    Also, someone ask you this sort of question, you get it wrong. The next time you get asked the question, you get the right answer.
  19. Apr 21, 2010 #18
    They may have changed the test in the years that I took it, but when I took it, I found that intuition was pretty much useless in taking the test. The problem is that the with intuition you could narrow down the problem to two answers on the multiple choice, but once you got to those two answers, you had to do the full calculation to figure out which one of the two was correct.

    EDIT: I just looked at the latest PGRE, and it doesn't seem that different from the one that I took. I hated the test because I found that I couldn't get very far with physical intuition, and I'm not that good at calculating things quickly.

    The other thing is that if I had to take the test right now, I probably wouldn't do that well on it. Give me two weeks of prep work, and I'll do fine. This suggests that the test measures something other then simple physical intuition (which is not necessarily a bad thing).
    Last edited: Apr 21, 2010
  20. Apr 21, 2010 #19
    First of all, there is a difference between can't do will and didn't do well. A huge amount of getting a high score on the PGRE involves just test taking skills, which can be learned. If someone gave me the PGRE right this moment, I'd totally bomb it.

    The thing about test taking skills is that are minorly important in grad school, but a lot less important than other skills. Also depending on the topic, physical intuition may or may not be important, and in any case you can teach intuition.
  21. Apr 21, 2010 #20
    What you need is to quickly isolate what is important, then you can solve most of the questions in ~20 seconds by just plugging some basic formulas that you should know. (And 20 seconds is on the far side, isolating what is important will take the majority of the time)

    At least I call that intuition, seeing the structure of the problem without doing it. It can be manifested in pictures such as "Which of these represents the correct acceleration in the following points" or it can be through problems that if you do it the normal way you need to calculate a lot but if you see through the problem then it is basically already done.

    But of course as said this is not a skill that is pivotal to success within physics grad school, it just helps.
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