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Studying Failing physics -- how can I improve

  1. Apr 1, 2016 #1
    Well i failed both physics exams. I am in physics 2 and guess what made an "A" in physics 1. My teacher curved our tests by 25 or more points and everyone made an A or B. So i have an instructor now who really teaches physics. Here is the deal, i studied very hard. Took notes on all classes, studied every problem in the homework and actually understood all the problems. But the problem is my instructor only gives us one or two scenarios and he asks a combination of them or a more difficult scenario on exams. He goes over maybe 1 problem that is similar but not by any means all inclusive. How do i succeed if i'm only given a few examples to work from? I even went out of my way to come up with problems on my own, read the entire chapters in the book and everything. If you want to make assumptions realize i am NOT lazy. I have a 3.2 GPA and study my ass off. Another issue, i don't understand the material. Here is an example of a problem.

    A single conducting loop of wire has an area of 7.2 x 10^-2 m^2 and a resistance of 100 ohms. Perpendicular to the plane of the loop is a magnetic field strength of 0.48 T. At what rate in T/S must this field change if the induced current in the loop is to be 0.32A?

    But why the heavy rearranging? This problem you have to rearrange the equation to get what you need. I can understand how that is done in this one scenario. But as soon as you swap it a little i dont know how to do it. What am i going to do? I cant be good at a subject with just seeing a few examples and say oh i get it now. Other students in the class are struggling but some students just get it probably because they had physics in high school. I never really had real physics so I'm stuck.
     
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  3. Apr 1, 2016 #2
    You could try forming a study group. See if you can get some of the students who are doing well to help with explanations or go over old homework and test problems with you. I know that when I was a lab assistant I was required to hold a couple homework study sessions for undergrads every week. Maybe your school has something similar.
     
  4. Apr 1, 2016 #3

    Student100

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    Rearranging an equation shouldn't bother you at all in physics.

    Changing the problem above a bit shouldn't bother you either - if you truly understand what you're doing. Since it does, it means you aren't studying correctly and aren't really understanding what the class is about.

    Why do these cause problems for you?

    Are you working problems by plugging in numbers right away? That's a bad practice, you should work with variables until you've isolated what exactly you need and have all the dependent information.

    Are you studying what the equations model? Their derivations? What different results mean? How variables are related or proportional to other quantities?

    Need some more information to help you.
     
  5. Apr 1, 2016 #4
    That is most of my problems. I dont understand much about the variables. I can distinguish what a problem wants and the equation but when i have to work through it like modify the equation to solve for what is being asked for or use algebra to eliminate this or that then i cant do it. What really kills it for me is the different scenarios. It seems like if you change a problem slightly that is like a whole new scenario. It is like studying nonstop all these separate scenarios and thinking i have it down only to see that i have no real understanding of the material. Also i am not plugging in numbers right away. Im trying to understand why the problem progresses the way it does. I make a best effort on that point. But it makes no difference it seems like with physics. Works in other classes but not here.
     
    Last edited: Apr 2, 2016
  6. Apr 2, 2016 #5
    Here are some tips I have. First identify what the problem wants you to find. Next make a list of what you "know" from the problem....I find that drawing a picture and labeling what I know is very helpful. Then identify what physical laws (i.e. equations) involve the variables that you are given from the problem, and which ones include "what you're looking for". Usually there is a list at the end of the chapter of important equations, or they're numbered or highlighted in the text of the chapter. This can be a good start to solving problems, though it isn't a fool proof approach. It can help you organize your information and thoughts a bit.

    For example, in the above problem I identify that it wants me to find the rate of change in a magnetic field, ΔB/Δt, that would be needed to produce a desired electric current in a loop. I notice that it gives me the value of that current, I=0.32 amps. It also gives me the area of the loop, A=0.072 square meters, the starting strength and orientation of the magnetic field B=0.48 Tesla perpendicular to the loop ∅=0 degrees, and the resistance of the wire R=100 Ohms. Some equations involving some of these things that are probably things you've gone over in class recently are Ohm's law V=IR, the expression for magnetic flux Φ which is likely Φ=BAcos∅ in your book...the expression for emf which is likely ε=-ΔΦ/Δt.

    As an aside: It is very important to know what these equations mean in words and concepts. Ohm's law says that the electric current produced in a wire is proportional to the electric potential (the voltage) causing it. This means that if you double the voltage, you get twice as much current...triple the voltage, you get three times as much current. In all science classes, each equation like this means something in words and concepts. The math is just a handy way of describing a deeper concept. It is absolutely vital to understand these concepts in order to do well in physics. As an example of why equations are preferred over sentences: notice that since the area of the loop isn't changing, and the orientation of the loop to the magnetic field isn't changing, that the only way the flux can change is if the magnetic field strength changes. So the previous sentence in math language is ΔΦ/Δt=(ΔB/Δt)Acos∅

    One thing to note is that the emf is voltage induced in the loop. It's important to also review definitions if there is some variable in an expression that you don't understand. ε=V

    A recap
    ε=V...which we got from understanding what emf is..... ΔΦ/Δt=(ΔB/Δt)Acos∅...which we got from Φ=BAcos∅ .....ε=-ΔΦ/Δt.....V=IR

    at this point you might have some "extra" equations that you don't need to solve the problem. This is where understanding the concepts behind the equations helps you to weed out the equations you don't need. We need all of these in this case. What you do next depends upon how comfortable you are with algebra. You can either manipulate the variables, or just start substituting in the actual numbers you know from the problem.

    ε=V .....ΔΦ/Δt=(ΔB/Δt)(0.072)cos(0 degrees)...the cos(0 degrees)=1 so this becomes ΔΦ/Δt=(ΔB/Δt)(0.072).....ε=-ΔΦ/Δt.....V=0.32(100)=32

    since ε=V, ε=32...and since ε=-ΔΦ/Δt we get ΔΦ/Δt=-32 So we have one equation left which just happens to include what we're looking for in the problem.

    ΔΦ/Δt=(ΔB/Δt)(0.072) which becomes -32=(ΔB/Δt)(0.072) and thus (ΔB/Δt)=-440 T/s...assuming I didn't make an obvious mistake somewhere...it helps to keep track of units to avoid making mistakes...it also helps to ask whether the answer you've found makes sense in the context of the problem....like if I had gotten -1,000,000 T/s, I might suspect I made a mistake.
     
  7. Apr 3, 2016 #6
    Thank you for your insight! I am not very comfortable with algebra and that is another big problem of mine and probably what separates me from the students that think this is easy. But anyway, the way to go about solving the problem you mentioned here seems very reasonable :)
     
  8. Apr 3, 2016 #7

    ZapperZ

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    And this is the root-cause of your entire problem : Math!

    You think physics is difficult, but you don't know that, because the source of your problem isn't physics, but your lack of tools to be able to solve the physics. I lost count on how many students I encounter that are struggling in physics because they lack the necessary mathematical skills.

    The ability to do algebra is REQUIRED to do physics. It is not negotiable. So is the understanding of trigonometry, geometry, etc. Without those, you have no way of doing physics. Students who are failing the class often are not able to do the math. There is just no way to do physics without knowing these basic math skills.

    You should not have been in this class.

    Zz.
     
  9. Apr 3, 2016 #8
    Yes but is it my fault that i am not prepared? Lets see the prerequisites for the class here. Physics 1. Well made an A in physics 1. Also college algebra, made barely a C in college algebra however. I blame the system. They green lighted too many people without them being prepared. Otherwise you wouldn't have so many people failing these classes. And you wouldn't have posts like these floating around

    http://talk.collegeconfidential.com/engineering-majors/1310761-failing-physics-for-the-4th-time.html
     
  10. Apr 3, 2016 #9

    Vanadium 50

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    You have two choices - you can stamp your feet and say "It's not fair!" (And you'd be correct) or you can learn the math and try again. Up to you.

    And you're right that you were not done a service by being passed without knowing the material. You might want to look at ratemyprofessors.com and see how popular professors who do this are, compared to those with strict standards.
     
  11. Apr 3, 2016 #10
    You can't just start blaming others for your difficulties! It's entirely up to you the rectify any issues you had in college algebra BEFORE taking physics.
     
  12. Apr 3, 2016 #11
    The system isn't perfect, but do you think people would honestly be okay if it were the other way around? Then the only difference would be that instead of seeing posts like that where people fail physics several times, we'd get posts that complain about people failing algebra several times, and I guarantee you that if that were the case, some people would find a way to blame the system for that too.

    At some point, students have to learn to recognize when they're having difficulties and work to correct them instead of blaming the system.
     
  13. Apr 4, 2016 #12

    micromass

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    Nope, it's not your fault. But it is your responsability to fix any issue you have with math. So better start soon.
     
  14. Apr 4, 2016 #13
    I will make a valid effort in that regard. I need to graduate some day! Gentleman thank you for commenting but we should end this now :)
     
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