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  1. E

    How does a permanent magnet lift iron filings

    Magnetic fields ain't like a hammer hitting a nail since the hammer does work. Magnetic fields are like the normal force on a ramp. It doesn't do any work since it's perpendicular to the displacement.
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    How does a permanent magnet lift iron filings

    I said that a magnetic field can't SPEED UP electrons and I stand by that. It can deflect them of course. The fact is that the force that a magnetic field exerts on an electron is always perpendicular to the trajectory (same as a satellite in a circular trajectory in a central force field) so...
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    How does a permanent magnet lift iron filings

    to krab: I finally found out what's the problem. The formulas you wrote for the energy and work are mechanical work. You still need to add the energy of the electric currents. If you do that then you'll get zero work. This is in one of Feynman's lectures, chapter 13 I think. I'm kind of busy...
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    Magnetic Monopole

    The fact is that no magnetic monopoles have been ever found (like a point particle being the source of a magnetic field). If there were any magnetic monopole it would explain why is charge quantized. More info: [Broken]
  5. E

    How does a permanent magnet lift iron filings

    Magnetic field don't work on any charged particle. This follows from the Lorentz force Law. If you want a proof just ask :D.
  6. E

    Introduction to Complex Analysis

    I think you should be familiar with at least some Calculus before trying to get into Complex Analysis. I don't know if you are by the way, I ain't familiar with european education
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    Calculators Which calculator to get? Ti-89, or HP49G+?

    In electrical engineering it's much more useful a TI 89 In civil/mechanical engineering I've heard that the HP rocks
  8. E

    Are certain integrals possible?

    If by "integrate" you mean finding its anti derivative as a combinations of the functions we already know, then nope.
  9. E

    How was e computed?

    calculate \lim_{n\to\infty} (1+\frac{1}{n})^n
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    How does a permanent magnet lift iron filings

    Hi I have no problem with the above, except that as far as I know \vec{N}=\vec{m}\times\vec{B} comes from the Biot-Savart Law as shown by Jackson's book on page 150. Furthermore, a magnetic moment is defined for a current distribution J (Jackson p.146) What causes me trouble is that I'm...
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    Computerized wave display

    If it's like using an oscilloscope, then you have to count how many divisions are in a single period, and with that you can calculte the freq. as well For the amplitude count how many divisions in the y axis does the waveform have
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    E/m question

    The field E between the plates is \frac{1}{\epsilon_0} \sigma in SI units, that should give you a hint
  13. E

    Life as a graduate student

    Thanks folks, keep'em coming
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    What's harder? Math, Physics or Engineering?

    You're correct, furthermore, we Engineers and Mathematicians are focused on different things, even when studying the same topic. Generally speaking, the engineer ain't that interested in the theory, he just wants to know how to solve something, with the mathematicians is the other way around...
  15. E

    So what is it, in that case?

    \int (1-x^2)^{1/2} = 1/2 ( x(1-x^2)^{1/2} + \arcsin x)
  16. E

    Good book on PDE

    This ones:
  17. E

    SHM Calculus Twister

    Ain't this same problem answered somewhere else on this same forum?
  18. E

    Table of Laplace transforms

    If it helps, the LT of the error function \frac{2}{\pi^{\frac{1}{2}} }\int_0^t e^{-u^2} du is \frac {1}{s(s+1)^{1/2}} And since you can always work with the N(0,1) distribution instead of the more general N(m, sigma^2) I think you'll find the aforementioned result useful. If you need the...
  19. E

    Table of Laplace transforms

    Schaum's intro to Laplace transforms has like 300 laplace transforms listed on a big table.
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    I would like to buy some software but not sure which one! Please help ;)

    Hi singleton. I've used both Maple and Mathematica (althoug not Calculus Wiz) and I would say that at the calculus level there isn't much difference. Say, you need to check the derivative of something, and the integral of some other function? Both will do the trick. In Mathematica (the...
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    Delta problem

    It depends on the voltage (current ) source connected to the circuit. Let's say you plug a 1 A source to the entire circuit I found out solving for the entire thing that the current trough the resistor of 6R is 1/34 R I wrote KVL for each mini loop, and then wrote KCL at the top, at...
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    Mental Calculation - How good are you?

    But how about calculating e^3 or e^{1.4} mentally? To find out how, read "Surely you're joking Mr. Feynman"
  23. E

    Some softwares for electronic engineering

    I find it more useful for electrical engineering the Texas Instruments calculators, especially the TI 89
  24. E

    What's harder? Math, Physics or Engineering?

    My personal experience is that it depends on one's personal abilities (Aside from departments, schools, universities). In Engineering they give you more [home]work, so you're stuck doing lots of stuff, some boring, some fun. The material ain't hard to understand. It's also important to be...
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    Life as a graduate student

    Hi, I would like to know how is the life of a graduate student, specially for PhD students, so I would really appreciate if someone could answer the following: What are your sources of income? If you have a fellowship/RA/TA, does your income cover for your expenses? If so, what is the...
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    Capacitor behavior over frequency

    I hate "hand waving" answers but here I go: In a capacitor you have a voltage because there are minus charges on one plate and plus on the other. On AC, you switch the polarity so the minus charges flow to the other plate over and over again. If you make the switching very fast, then the...
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    How does a permanent magnet lift iron filings

    Thank you for your input krab, I'm still not convinced, but I'll go through your argument with more detail later nonetheless.
  28. E

    Ampere and charge density

    I think you should have some extra information to get the \frac{dL}{dt}. For instance, some info like L(t)
  29. E

    The Swing Problem:How can you go completely around?

    Sorry, I meant gravitational force, I was thinking of something else. And the fact that velocity ain't constant means that there is a tangentical acceleration as well, so you have to take that into account in Newton's 2nd Law.
  30. E

    Rational Number Help

    Krab is right provided that you define x^{-1} =u and the like for y and z and work with those auxiliary variables