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Can a material stay magnetized after current is switched off in an electromagnet?

  1. May 21, 2009 #1
    Hi everyone,
    Is there a material which, inside a solenoid, immediately or in a very short period of time gets magnetized as current is switched on and then stays magnetized for a while if the current is switched off? For if this were true then this would mean we could derive more energy out of the system as we put in. We magnetize the material, switch off the current then use that magnet to attract magntic material to it and derive energy from it. Then as the material is demagnetized after some time we can with much less energy remove the materials which were initally attracted to the temporary magnet. Then repeat the process. Wherein lies the problem?
     
  2. jcsd
  3. May 21, 2009 #2

    tiny-tim

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    but wouldn't the presence of that magnetic material resist the current, so that it magnetised the magnet less in the first place, thereby losing energy?
     
  4. May 21, 2009 #3
    Permanent magnets are made by the process you describe. Every ferromagnetic substance will retain magnetic field due to hysteresis. Now you say we take an inductor put in magnetic energy, switch of the current. Now when you are putting in magnetic energy[1/2Li^2] this energy is not being given back to the battery rather it stays in the inductor and this is the enregy that is being used to attract magnetic materials.
     
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