4 ms·

Here are some more items I can think of: speakers, earphones, magnetic switches (eg. laptops), relays, sensors, CD/DVD ROM, maglev.

• beaconstudios 9y ago
  AFAIK they all use electromagnets rather than permanent magnets.
  • AlexandrB 9y ago
    Last time I checked speakers and headphones still had a single permanent magnet + an electromagnet. However, for speakers, the "old" iron permanent magnets generally work just fine - they just have to be bigger.
    • dahauns 9y ago
      "Just have to be bigger"? I want lighter guitar amps that don't cost an arm and a leg, dammit! :)
      • bsder 9y ago
        Then go solid-state. Inverter-based power supplies are sufficiently light that a guitar amp should only be the weight of the wood and the speakers. And, the speakers have to be a certain size to move the correct amount of air--so the copper coil is probably the limiting weight. It's remarkable how much air you have to actually move to get decent sound volume.
        • dahauns 9y ago
          Hm...sounds plausible from a physics POV, but maybe there's something else? Since, in practice (at least as far as I can speak from experience), old-school ferrit 15" speakers are ~7-8kgs, while you can get similarly specced neodymium speakers that weigh about half (3-4kgs).
          • bsder 9y ago
            Maybe ferrite, but you can also get ceramic magnets: Ceramic 4.4lbs 50W http://celestion.com/product/20/rocket_50/ http://celestion.com/product/20/rocket_50/ Neodymium 3.7lbs 60W http://celestion.com/product/14/g12_century_vintage/ http://celestion.com/product/14/g12_century_vintage/ And, yes, you will find that the values are all over the map in terms of weight. There are some much less powerful speakers that are quite a bit heavier.
  • dEnigma 9y ago
    At least earphones and speakers use permanent magnets[1], though according to Wikipedia[2] the early ones actually used electromagnets. I agree though that relays and maglev use electromagnets. I'm not sure about the rest. [1]http://www.physics.org/article-questions.asp?id=54 http://www.physics.org/article-questions.asp?id=54 [2]https://en.wikipedia.org/wiki/Loudspeaker#History https://en.wikipedia.org/wiki/Loudspeaker#History
    • Robotbeat 9y ago
      Some types of Maglev use permanent magnets: https://en.wikipedia.org/wiki/Inductrack https://en.wikipedia.org/wiki/Inductrack
      • dEnigma 9y ago
        Oh, interesting. I didn't know about any project like this; thank you for the link.