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Measuring magnetic field of a solenoid relative to distance

  1. Feb 26, 2015 #1
    So, I recorded the result of a LabQuest 2 Vernier Magnetic Field Sensor on different points of a plane, with a solenoid in middle with a 5 amp current running through. I want to compare my results with theory, but have no idea what equation i'm supposed to be using.

    I assumed it was B = μ0ηI/r3

    where μ0 is the magnetic constant(4π * 10-7), η is number of turns of the solenoids/ the length of the solenoids wire (570 turns/216 meters), I is 5 amp current, and r is the distance between the point where i measured using the magnetic field sensor and the center of the solenoid accounting for the z displacement of the plane from the center.

    But I guess I was way off. I have no idea what equation I'm supposed to be using is.

    It seemed correct from what little I guess I know about magnetic fields, but the results I get from the equation are obviously wrong. I made sure to move away other magnets that may interfere with the experiment and calibrated the sensor. So, there shouldn't be too much wrong with the results from the experiment and it behaved the way you'd expect a magnetic field to behave. There probably still is a margin of error in the measurements, but the equation is what's obviously wrong one.

    the purpose of the experiment was to compare results with theory. I can't really do that without proper theory. Anyone know the proper equation to compare the results to use for this? I'm at a complete lost.
  2. jcsd
  3. Feb 26, 2015 #2


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    Staff: Mentor

    The Wikipedia article about solenoids has what appears to be the most general formula:


    At points far enough away from the solenoid that it "appears" to be small, it should behave at least approximately like a magnetic dipole. Many textbooks, web pages, etc. discuss the magnetic field of a dipole, so you should be able to find it easily with a Google search.
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