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Why does an Electromagnet Vibrate ?

  1. Apr 9, 2010 #1
    Why does an Electromagnet Vibrate ???

    whenever any iron plate or steel spoon is placed near permanent magnet(not of very high strength) it gets attracted towards it and when it is removed from it it removes easily without any vibration effects.

    but if the same thing is performed with electromagnets then we experience a vibration in the spoon both during attraction and during removal of spoon from the field. Also a light humming sound is also there.

    why does this vibration happens ??
    is there any way to remove this vibration effect in case of electromagnets and let it behave like permanent magnets?

    also if AC supply is used in electromagnets(in place of DC supply) then this vibration effect and humming sound is more.

    what is the reason behind this phenomenon??
     
  2. jcsd
  3. Apr 9, 2010 #2

    vk6kro

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    Re: Why does an Electromagnet Vibrate ???

    An iron object held near an electromagnet will vibrate if the field from the electromagnet is varying.

    This will not occur if the electromagnet is getting steady DC as from a battery but it will happen if the electromagnet is getting pulsing DC, or AC.

    It will get pulsing DC if the output is taken directly from a rectifier without any filtering.

    Like this:

    500px-Halfwave.rectifier.en.png

    You can see how the voltage is varying in both the AC input and the pulsing DC output and either of these will result in a varying magnetic field if applied to an electromagnet, so you would get vibration.
     
  4. Apr 10, 2010 #3
    Re: Why does an Electromagnet Vibrate ???



    yes you are right (this is what principle says) but as u take the iron piece towards the field or if you touch the piece magnetically attached their is a kinda vibration along with humming sound (just give it a try practically) in case of electromagnets but the same is not present in case of permanent magnet.

    i think it's coz of generated flux but not sure.

    i just want both of them to behave in same manner...............is there any known method
     
  5. Apr 10, 2010 #4

    vk6kro

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    Re: Why does an Electromagnet Vibrate ???

    i just want both of them to behave in same manner...............is there any known method


    Yes, you would have to run the electromagnet from pure DC, not pulsing DC.

    If the electromagnet would work on 12 volts, you could just connect it to a car battery.

    Or, you may be able to smooth the power supply by adding an electrolytic capacitor across the electromagnet.
    These have to be connected the right way around (+ve marking to the +ve supply) and the actual capacitor would have to be chosen to suit the electromagnet.

    Do you know what voltage it runs on and how much resistance it has, or how much current it uses?
     
  6. Apr 10, 2010 #5
    Re: Why does an Electromagnet Vibrate ???

    An electromagnet will behave the same as a magnet only when you power the electromagnet from a true DC source, such as a battery. If it is powered from a simple home-made DC power supply, then you're apparently getting some "ripple" current into the electromagnet - a portion of the AC waveform is still present at the output of the power supply. This time-varying current is what is causing the time-varying magnetic field that you feel. Adding a very large capacitor to the output of the power supply will reduce, but not eliminate, the ripple. A high quality electronically-regulated power supply can come much closer to an ideal DC source, but a battery is simpler and cheaper.
     
  7. Apr 10, 2010 #6
    Re: Why does an Electromagnet Vibrate ???

    fin i tried the way said by using true DC Supply through a battery.

    it did worked, the vibration was lesser as compared to AC converted to DC supply but in this case the strength was weaker.

    AC to DC source 12 V, 3 Amps logically 36 watts i.e at max i can draw 3 amps @ 12 V from it.

    DC battery 12 V 500 mAh

    coil resistance 40 ohms

    mathematically it should draw 0.3 Amps from either of the sources for producing the field then why am i finding weaker strength.

    this should not happen theoretically but practically i am finding it.

    m gonna giv a try via capacitor arrangement..........in this possibly the vibration must dampen without reducing the strength.
     
  8. Apr 10, 2010 #7

    vk6kro

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    Re: Why does an Electromagnet Vibrate ???

    Do you have a voltmeter? Check the voltage from the power supply.
    It is possible that that power supply is delivering more than 12 volts average because there is not much current flowing.

    If it is giving an average of, say, 15 volts, the peak value of the pulses coming out of it will be about 21 volts. If you put a capacitor across the output, the voltage will rise to around 21 volts as well as being smoother.
    This will certainly make your electromagnet more powerful. The current in it will rise to about 0.5 amps.
    Check that it doesn't get too hot. It will be dissipating about 11 watts, which could make it get quite hot.

    The capacitor should be in the range of 1000 uF to 4700 uF and rated for 40 volts.
     
  9. Apr 11, 2010 #8
    Re: Why does an Electromagnet Vibrate ???

    yeah finally i got it ........ minimal vibration and humming sound. though the strength of the magnet wasn't so strong but still it worked.
    i think i must increase the no. of turns of the coil along with voltage of the source for more stronger electromagnet.

    thanx anyways
     
  10. Apr 11, 2010 #9
    Re: Why does an Electromagnet Vibrate ???

    thanks guys for ur responses
     
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