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Earth's Magnetic Field Experiment / Helmholtz Coils?

  1. Oct 3, 2012 #1
    1. The problem statement, all variables and given/known data
    In my ab, we were supposed to obtain the horizontal component of the earth's magnetic field by measuring the period of oscillation of a bar magnet in a known field using the Helmholtz coils, a resistor, and an AC power amplifier. Now during this experiment I had issues with the measuring the period. The reason for so, is because my period of oscillation when applying 1 voltage to the coils would be higher than no applied voltage. And yet when I apply 2, 3, 4, or 5 voltages to the initial 0 applied voltage of the Helmholtz coils, the period of oscillation would decrease (like it's supposed to).
    Therefore, my question is:
    Why is it when I apply 1 voltage to the Helmholtz coils the oscillation slows down, but when I apply additional voltage to that, the oscillation will speed up?


    2. Relevant equations



    3. The attempt at a solution
    I don't understand why it would slow down only when I add the 1 voltage, and not when I add the additional voltages. Therefore, I would know I did something completely wrong. However, according to my Lab instructor I did everything correctly.
     
  2. jcsd
  3. Oct 4, 2012 #2
    In a magnetic field coil, it is the current that matters, not the voltage.

    Did you try negative currents/voltages?

    Did you try to rotate the setup?

    Have you estimated the magnetic field of your coils for the currents/voltages applied?
     
  4. Oct 5, 2012 #3

    rude man

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    How is the magnet suspended in the coil? How do you keep gravity from affecting the results? You need to describe the setup more fully.
     
  5. Jan 17, 2013 #4
    hello i am new in this forum and would like to get some help,
    Inside a helmoltz coil exist a magnetic field value due the earth magnetic field, that is without inducing any current to the coils,right?. Now if I want to induce a current in the coil to generate a specific magnetic field value,Does the resultant magnetic field is the sum of the two magnetic field values (magnetic field without current + magnetic field with current) or it is the specific magnetic field produced by the current only?.
     
  6. Jan 17, 2013 #5

    rude man

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    The magnetic field inside the coil is the (vector) sum of the Earth's field plus that induced by any current applied to the coil.
     
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