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Calculation of Electric field Density(easy question, please help )

  1. Jan 5, 2009 #1
    Calculation of Electric field Density(easy question, please help!!)

    1. The problem statement, all variables and given/known data
    Problem : There is a 1C point charge on (0,1) positive y axis, and a 2C point charge on (0,-1) negative y axis. find the location where the electric field intensity is zero.


    2. Relevant equations
    E = Q/4*PI*e*r^2


    3. The attempt at a solution
    It's so simple!!! The answer is (0,3-2*(2^1/2)), or approximately, (0,0.2).
    This is actually an exam question. I am so darn sure that the answer is (0,0.2) and so does 90% of the students in class, but the professor keeps on saying he's 100% sure it's on the negative y axis (0,-0.2). How could he be so stubborn when 90% of the student in his class come up to him with the right answer? Honestly, I don't really understand how he became a professor...

    Anyway, this is very important for me because my grade would go one level down if I get this question wrong, and the professor tells us to bring sometime good enough to persuade him. I was searching for ages for something like an electric field calculator, but all I can find is java applets that only show the electric field lines, not the results in numbers. I know that the lines are sufficient enough to make someone believe that the E is zero at (0,0.2) but this professor just won't listen, so I might have to bring him a program with numerical calculation results. Do you have any suggestions for this? It doesn't have to be a program, but anything strong enough to make the man admit that he was wrong and accept the truth(i.e. a similar exercise example in a well known school textbook would be nice).
    Please help!!!
     
  2. jcsd
  3. Jan 5, 2009 #2

    Hootenanny

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    Re: Calculation of Electric field Density(easy question, please help!!)

    Any and all undergraduate texts should have exemplar calculations of this type. To be honest you 'Professor' should know that his answer is incorrect without any proof, it is quite obvious that the point where the electric field is zero must be closer to the smaller charge.
     
  4. Jan 6, 2009 #3
    Re: Calculation of Electric field Density(easy question, please help!!)

    Oh my god this guy is killing me... I downloaded a program called 'Electric Field' which calculates, and shows the directions of the electric field and I showed him 'Visually' why E has to be 0 near the smaller charge, but this is what he says.

    'No, no, no, don't bring any of this. I want to see the exact same question/answer in a textbook written by one of the famous people in the electromagnetic field.'

    Are you F***ing kidding me??? I just SHOWED you a visual proof and yet, you still deny??????
    I was almost about to say that. So he wants an exact same type of problem in one of the textbooks used in colleges, so I searched the next downloading about 10 textbooks or so, but I could only find problems that that considered F=0, not E=0. I know, the results are obviously the same whether it be F or E, but he is too stubborn to accept that fact so I'll have to look for an alternative...
    Does anyone still have any suggestions? Thanks in advance.
     
  5. Jan 6, 2009 #4

    Hootenanny

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    Re: Calculation of Electric field Density(easy question, please help!!)

    This is ridiculous. Have you tried showing him your work and asking if he can point out where you've gone wrong?
     
  6. Jan 6, 2009 #5

    Redbelly98

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    Re: Calculation of Electric field Density(easy question, please help!!)

    I would go to another professor in the department. Obviously this guy does not respect what students think. Maybe he would listen to a colleague. Or the head of the department (hopefully that is not him.)

    Like Hootenanny said, obviously the answer is closer to the smaller charge, on the +y axis.
     
  7. Jan 6, 2009 #6
    Re: Calculation of Electric field Density(easy question, please help!!)

    It is indeed ridiculus. I gave him a note with 3 concrete proofs of why it should be on the +y axis. He said he will look into it, But I believe he'll throw it in to the trash as soon as he gets to his lab.

    This question was actually in a Japanese textbook. The solution assumes the the E=0 point(A) is in the -y axis, and sets the distance between the O point and A to (D). The result of the calculation is D = -0.2. If D = -0.2, and A was assumed to be on the -y axis, then converting it to cartesian cordinates would obviously result in (0,0.2). But this guy keeps on saying (practically yelling) that one must use the absolute value of D, and not D directly, and I ask why. He says 'Because it should be like that'.
    Because it should be like that?????? LOL.

    Then I ask 'But professor, isn't that ignoring the fundamentals of math? Math and Electromagnetics should be very closely related, and ignoring either one would result it failure of the other.' and his answer is one of the funniest things ever that could come out of a professor's mouth. 'Well, you have to ignore math sometimes and only accept the truth. The people from the old ages defined these things and I have no power to change them.'
    WTF?????? I really want to beat this guy hard until he starts whining like a baby and admits that he is wrong.

    I guess all I can do now is pray, and wait for the results tomorrow.

    I already did that, and brought him a solution from another professor, but this is what he says.
    'That's what he thinks, and he might be wrong. You have to give me a more solid proof.'
    LOL... I've never seen somebody so narrow minded in my entire life...
     
  8. Jan 7, 2009 #7

    Borek

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    Re: Calculation of Electric field Density(easy question, please help!!)

    Looks like you may have to go up the ladder then.
     
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