Search results

  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.
  2. E

    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...
  3. E

    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...
  4. E

    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: http://budoe.bu.edu/~corth/monopole_faq.html [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

    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...
  7. E

    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.
  8. E

    How does a permanent magnet lift iron filings

    I don't want to get into baryons and the internal structure of neutrons because that's off topic. All I'm saying is this: the force on a magnetc dipole is derived from the Loretz force law, which means that the magnetic force does not work. The point I'm trying to make is that Lorentz...
  9. E

    Several Questions on Electric Potential

    Electric Field: \def\vr{\mathord{\vec r}} \providecommand{\abs}[1]{\lvert #1 \rvert} \vec E (\vr) = \frac{1}{4 \pi \epsilon_0}\int\frac{\rho(\vr\ ')(\vr-\vr\ ')}{\abs{\vr-\vr\ '}^3}d l' Electric potential: \def\vr{\mathord{\vec r}} \providecommand{\abs}[1]{\lvert #1 \rvert}...
  10. E

    The direction of the electric field at point P is +x direction

    And by Newton's 3rd Law, the force exerted by the particle on the ring is the same in magnitude but of opposite sign of what AKG computed.
  11. E

    Repelling force of magnetism

    The Froglev http://www.hfml.kun.nl/froglev.html [Broken] http://www.sci.kun.nl/hfml/frog-ejp.pdf [Broken]
  12. E

    How does a permanent magnet lift iron filings

    So you're talking about fiticious magnetic monopoles? Because a real magnet is made up of tiny magnetic dipoles which are nothing but tiny currents, which are composed by charges with a certain velocity. If we're talking about forces on magnetic dipoles then said force is F=grad(m B) but...
  13. E

    How does a permanent magnet lift iron filings

    To bring the magnets together requires changing the magnetic field, and a changing B induces an E. Against this E is the work done. At the beginning and at the end there is no E, but in between there is definitely one.
  14. E

    How does a permanent magnet lift iron filings

    I'm afraid I'll have to disagree Magnetic forces do not work since F= q (v x B) is a vector perpendicular to the infinitesimal displacement dr, so W= F dr=0 Back to the original question, magnetic forces change the direction of another force. When lifting something, the one doing the...
  15. E

    Question about this situation with two point charges +Q and -Q

    As I see it, if you have 1 plus charge and 1 minus charge, you'll have an electric field between them. If you place a metal rod between them, then the plus charges of the rod will be pulled towards the - charge and the negative charges of the rod will go the opposite way. You'll have one end of...
Top