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Everything posted by kevinalm

  1. And in high current relays and and switches. But a permanent magnet won't work with an AC current. You need to use an electromagnet so that the cross product of the current element and the magnetic field doesn't reverse 60 times a second.
  2. The arc is probably ac, so the direction of deflection reverses many times a second. No noticable net deflection will be seen. Try with a dc arc welder.
  3. It was something fun. Glad to have helped.
  4. Something more along the lines of what the op had in mind. There exist optical media that are nonlinear, whose index of refraction is strongly dependant on intensity. If you make an interference cavity out of such a media and setup a destructive interference with a strong monochromatic light source (laser), then you can feed a much weaker 'signal' that varies the output (by changing the index). You then have a light amplifier. I recall reading about it some years ago in an article on 'photonic circuits'. It was proposed as an all optical analog to the transistor. I don't know if anything ever came of the idea. I do believe some actual experiments were done. Sorry, don't have a link.
  5. Just out of curiousity, why did you fill an emu egg with H2? Sounds like something fun.
  6. kevinalm


    Most of the cable vibration/oscillation dampers I have seen are diamond shaped nearly flat shiny metal, about a foot or so across. But that is another possibility.
  7. What's the volume of an emu egg? Less than a liter? Call it a liter. IIRC ~22liter equals a mole of a gas at stp. So 2 x 0.05 mole of HCl for a little over a liter of H2, very roughly. 100ml of 1M or 200ml of 0.5M HCl should do nicely. Depends on how fast you want it to react. Maybe you'd want to go larger quantity of less concentration, its been a long time since I've handled HCl so I'm just guessing as to a reasonably safe concentration to handle.
  8. Kind of a long shot, but interference perhaps? Like the rainbow effect of a soap bubble or oil film in sunlight. The pane thickness is awefully large for that, and window glass isn't all great a plain, to form a uniform color. Does the color change as you change veiwing angle?
  9. kevinalm


    Was there an airfield or airport nearby? I have seen brightly colored plastic balls on a powerline (half red/half white about a foot in diameter) used as a visual obstruction warning in the landing/takeoff path of a small dirtstrip runway here in the US.
  10. kicker, this should interest you. http://www.phys.uu.nl/~thooft/theorist.html Have fun.
  11. First and formost, it prevents the bullet from tumbling end over end. Tumbling causes the point of impact to be more randomized. Kind of like a falling leaf fluttering to and frow as it falls. Also, the axial spin along the line of travel evens out the effect of any surface imperfections, further reducing the 'falling leaf' effect.
  12. Not thrilled with the new sample format. I have to scroll side to side to see the far right edge. I'd rather use the scroll wheel to go up and down.
  13. Ok, I'll put you out of your misery. Any room number that appears once on the list would allow the professor to know immediately the answer, because he knows the room number. So...
  14. Well, since the op has apparently solved the problem, I will give a clue that almost, but not quite, gives it away. With the table of room numbers and ages in front of you, ask yourself the following question. How was it possible for the professor, who _did_ know the room number, to _not_ know the answer until the clue about the eldest child? The answer is right in front of you. (assuming you didn't miss a age/room combination.)
  15. Ha, cracked it. And there are no 'red herrings', although the sentence about the violin is disguised. All three pieces of information are critical. As this is homework, I hesitate to give too big a clue, but start by explicitly writing out all allowable combinations of ages and their products. ie 1*2*10=20.
  16. IIRC,there was some concern about N N fusion reactions. After determining the cross sections of the possible reactions, it was realized that the atmosphere simply wasn't anywhere near dense enough for a sustained fusion burn wave.
  17. In the US, all "lime" for agricultural/garden use is calcium carbonate. (powdered limestone). To get CaOH you would have to specifically get "slacked lime", which isn't very commonly available. Kind of a lift = elevator language thing going on I think.
  18. Here's a website you should check out. http://www.phys.uu.nl/~thooft/theorist.html
  19. Generally speaking, the resonant frequency of a harmonic oscillator is only amplitude independant if the restoring force is linear, ie of the form F=-kx where k is a constant. Which of course is why a pendulum is amplitude dependant, the restoring force only satisfies this condition approximately, to the extent that the small angle aprx. sin x = x holds.
  20. Here's a link: http://farside.ph.utexas.edu/teaching/336k/lectures/node38.html Fitzpatrick explains it pretty well.
  21. It probably wouldn't be practical for moving a ship, but how about a fluidyne engine/pump? http://en.wikipedia.org/wiki/Fluidyne
  22. The outgoing wave induces currents in the conductive plate. These currents are phased such that in the absence of the outgoing wave a bidirectional plane wave would be emitted 180 degrees out of phase, both into and out of the microwave. Sum that with the original outgoing wave and you have zero transmitted and 100 percent reflected. Punching holes in the plate disturbs the current flow and interferes with both the cancelation of the transmitted wave and creation of the reflected wave. This isn't too bad until the hole size approaches wavelength, then the behavior switches quickly to transmission. I'm not entirely clear on why, but iirc it relates to diffraction and Raliegh effect, and to interference for an array of holes. Given that the quanta for a microwave photon would be on the order of 10^-5 ev, I can't imagine that any discernable quantum mechanisms are involved. I suppose if you cooled the interior of the oven with liquid He and... Of course you could always create a coresponding quantum description, but classical E/M is quite able to handle it, with a little wave optics thrown in.
  23. Have you ever been to this website. Lots of free downloadable lecture notes you might enjoy. http://www.phys.uu.nl/~thooft/theorist.html
  24. I was recently reading some online lecture notes on classical mechanics that said basically the same thing. That a poor choice of coordinate system can make a solution virtually unrecognizable. It was an analysis of the motion of a pendulum bob in 2 dimensions. The original answer was a mess, but simply rotating in the x-y plane turned it into the standard equations for an elipse, circle or line, depending on the major and minor axis parameters.
  25. Actually, it is not generally true that E and B are perpendicular, even in induced fields. It _is_ true for the far field (self generating portion) of a plane E/M wave.
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