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What typical voltages are induced from a typical magnet (50-75 gauss)

  1. Apr 30, 2012 #1
    Hi, I'd like to use a millivoltmeter to research voltages induced from a basic ceramic magnet brushing by a conductor. So, I need to buy a millivolt meter. What voltage ranges will be required, and what read-rate should the millivolt meter have (in order for it to register the voltage in a split second brush with the magnet)? Is 1 millivolt a reasonable value to expect?
    Any sources (books or online) you know I should check out related to this question?
    Also, it would be nice if it would record these voltages (or at least leave it displayed so I could record them). Can you suggest any particular model millivolt meter?
  2. jcsd
  3. Apr 30, 2012 #2


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    Staff: Mentor

    What is a "typical magnet"? Field strength is not even a parameter of the electromagnet itself.
    Which type of experiment do you plan to perform?

    Without these things, it is impossible to give any number.
  4. Apr 30, 2012 #3
    If you just want to show that a moving magnet can produce an induced emf then you will need a sensitive milliammeter or micro-ammeter. I would suggest an analogue meter so that you can see movement of the pointer. A digital meter might be difficult to interpret.
    If you have access to an oscilloscope that should also give some indication and you may be able to store the information.
  5. Apr 30, 2012 #4
    Thanks for the reply truesearch... astute observation about the analog meter--probably right about that. And yes, I should probably be in the micro amp range to be sure to be sensitive enough. An oscillascope also would be great, but I do not have access to one, saving the data would also be ideal. Glad you were able to have a sense of what I was looking to find out. Thanks.
  6. Apr 30, 2012 #5
    Thanks mfb for the reply,... by a typical magnet, I mean a permanent, ceramic magnet in the 50-75 gauss range, not an electro-magnet. The experiment I have in mind is to brush the permanent magnet across an insulated conductor (steel or copper) with different orientations of the permanent magnet in relation to the conductor (north-south direction oriented with the conductor--parallel or perpendicular), and record the various results.
    I should probably use faraday's law to estimate the voltage, but I get confused when I try to appy it to this situation. I guess the number of turns would be 1. so you'd just have E = d(BA)/dt. B would be the magnetic field strengh, but A is the area? If the wire is straight where the magnet passes by, What area? Isn't the area usually the area of the coil? I guess it should have something to do with the distance of the magnet from the conductor--possibly. I guess B would go from 0 --> 50 gauss (is that the right units to use)? So, again, any help you can be regarding what range the voltmeter should be in, or possibly I should be observing the amps? And an appropriate (and cheap) model to use would be greatly appreciated.
  7. Apr 30, 2012 #6
    Let's try using Faraday's Law:
    [tex] \oint E \space d \ell = V = -N \int n \cdot \frac{dB}{dt}dA [/tex]
    N=100 turn coil
    A=0.0005 meters2
    dB=0.0075 Tesla
    dt=0.1 seconds

    V = 100 * 0.0005 * 0.0075 /0.1 = 3.75 millivolts

    This is a very short pulse.
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