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Electromagnet not working

  1. Nov 21, 2009 #1
    Dear Guru Engineers,

    I made 650 coils round a ferrite rod of cirumference about 2cm using super thin (like hair) copper wire that is insulated by some kind of yellowish golden orangy 'lacquer'. I hope you get the picture what i am trying to describe here :p

    Anyways, i used a strong magnet and oscillated it up and down the shaft of the ferrite rod.

    I sandpapered the ends of the wires terminating on the rod and hook them up to the amp-meter. nothing. seemed like no current produced at all??

    pls could you explain what could be the problem and was my method wrong?

  2. jcsd
  3. Nov 22, 2009 #2


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    Staff: Mentor

    Moving the magnet up and down the mid-shaft area doesn't change the flux through the turns. Try wiggling the magnet at one end of the rod.

    Also, put your meter on an AC Volts setting. You will see the induced EMF from the changing flux through the coils.
  4. Nov 22, 2009 #3


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    Science Advisor

    And check the resistance of the coil.
    You may not have removed the insulation doing it like that.

    I lay the wire on a hard wood surface and scrape with a razor blade until I can see copper and solder to it.

    cleaning wire.PNG
  5. Nov 22, 2009 #4
    Dear Berkeman & Vk6kro,

    I am very grateful for your explanations. This forum rocks!
    I never knew the output was AC . 8)
    Will try again.

    Best regards
  6. Nov 22, 2009 #5


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    Science Advisor

    If you approach the end of the ferrite rod with one pole of a strong magnet, the output will be DC until you reverse the direction of the magnet or stop moving the magnet (when you will get nothing).

    Your meter will be more sensitive on the DC ranges because the AC range has a diode in series with the input.

    So, try it on DC volts first until you get some sort of a reading. If there is a 200 mV range, try that first.

    Then, you could try putting a voltage on it and seeing if you can deflect a compass needle or pick up small nails etc.
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