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Lifting magnet ?

  1. Jun 4, 2008 #1
    I want know that lifting magnets for lifting a lots of cars ; so it use energy or not?

    Why a lifting magnet use energy?

    It can only have a static force with his superconductor !
    Why that superconductor use energy(electricity) for his static force?

  2. jcsd
  3. Jun 4, 2008 #2
    Those are electromagnets.. they temporarily behave as magnets while current is passing through them and their magnetic filed intensity can be changed depending on a number of factors.
  4. Jun 4, 2008 #3
    Don't forget that work must be done to pull the car off the ground.

    Work = Force * Distance

    Work is a synonym for energy as far as I know.
  5. Jun 4, 2008 #4
    OK i know that force is not Work !

    i only want know that big supercodactors for lifting big irons use energy or now?

    if they use so please explain that why they use energy for lifting ...
    (i know that supercondactors have not resistance or have very thin resistance !)
  6. Jun 4, 2008 #5
    >>>>attention that i want only electromagnet be a magnet and lift the car or drop down it ...
  7. Jun 4, 2008 #6
    Separate the two types of magnets. An electromagnet is convenient but uses energy to produce the magnetic field (even if it's a superconductor, it uses energy - just in a less straightforward manner). So, if you use an ordinary magnet (albeit a very large one) to lift a car, it is easier to think about and you can see there are two points at which work is done. When the magnet nears the car and attracts the car, work is done in the metal of the car. When the crane lifts the magnet attached to the car, the crane does work.

    The thing you probably want to focus on is the changing magnetic field in the body of the car. That will always be an energy drain. You can somewhat disguise this work by making it subtle, but you will always have both a hysteresis loop and a Fd term at the minimum.
  8. Jun 4, 2008 #7
    so electro magnets use energy when the ELECTRIC is swing around the electromagnet by resistance
  9. Jun 4, 2008 #8
    I don't understand your statement, so can't answer it. Can you please restate it in another way.
  10. Jun 4, 2008 #9


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    Yes energy is wasted by the heat generated when current flows through the resistance of the wire coils in the magnet. Superconducting magnets don't have resistance and so don't waste as much energy.
    There is also energy wasted in the metal body of the car, the magnetic field causes current to flow in the metal of the car which has resitance and so wastes energy as heat.

    There is also work done by the crane which then ifts the car - but this is the same if a magnet or a hook is used.
  11. Jun 4, 2008 #10
    SO if the lifter builded by superconductor it don't use energy !
    OK i understand that

    So the energy of lifter spended on the Car !?
    So if we build a car with superconductor ; So the energy of lifter don't waste with car resistance ? (because our car that lifted by superconductor lifter ; builded by superconductor and so it have not resistance and it don't waste energy)

    i'm true?
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