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What is the induction at infinity ?

  1. May 20, 2007 #1
    What is the induction at infinity ?
    I told teacher it to be 0 but she disagreed.

    Using the formula for calculating induction and substituting big distances into the formula gives me also 0.
    Is my teacher stupid ?
     

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    Last edited by a moderator: May 20, 2007
  2. jcsd
  3. May 20, 2007 #2

    Doc Al

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    Staff: Mentor

    Induction of what? I have no idea what that graph represents. Please present the entire question with all needed background info.
     
  4. May 20, 2007 #3
    Magnetic induction.
    It is produced by homogeneous solenoid.
     
  5. May 22, 2007 #4
    Any feedback ?
     
  6. May 22, 2007 #5

    Doc Al

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    Staff: Mentor

    Are you asking about the magnetic field outside of a solenoid as distance goes to infinity?

    What formula did you use? What does that graph represent?
     
  7. May 22, 2007 #6
    I had a solenoid and its lenght was 0,222 meters. The diameter of the solenoid was 120 mm.
    My goal was to measure the magnetic induction of the solenoid at solenoid axis. The current that runs through solenoid is a sinusoidal AC.
    The coil was used to measure magnetic induction. At the axis
    the voltmeter shows me that at the center of solenoid the voltage is about 0,40 Voltage. Moving away from the point at center reduces the voltages. In other words about 12 cm away from the center shows me that the voltage is 0,18 V. Why does moving away from the center point at solenoid reduces voltages ?
    The formula for calculating magnetic induction at certain distances from the center point was:
    induction = (l/2 - x)/sqare root((l-2x)^2+D^2) + (l/2 + x)/sqare root((l+2x)^2+D^2) where l is length of solenoid and D is diameter of solenoid.
    The condition l >> D is not satisfied.

    I was told that magentic field was homogenous. Why does the voltages reduces if magnetic field is homogenous ?

    Let me put my problem into other words.
    Let's discuss what happens to solenoid when current runs through.
    In physics, the term solenoid refers to a loop of wire, often wrapped around a metallic core, which produces a magnetic field when an electrical current is passed through it. As for solenoid I was using to do my experiments in order to calculate the magnetic field I want to ask the following.
    Because l << D is not satisfieid I suppose that the current which flows through loop of wire is the same everywhere where the current passes.
    If we look at this solenoid, which is 20 cm lenght. Is it right to say that choosing one point on this solenoid's wrap produces different induction current if we go away from the point we consider the situation ?
     
    Last edited by a moderator: May 23, 2007
  8. May 23, 2007 #7
    Any help within 3 hours would be highly appreciated.
     
  9. May 23, 2007 #8

    Doc Al

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    Staff: Mentor

    That's not much of a solenoid--generally solenoids have a length much greater than the diameter, assuring a relatively homogenous field inside the solenoid.
    Your solenoid is only 22.2 cm long--moving 12 cm from the center takes you outside the coil!
    The magnetic field is homogenous inside a solenoid--that's not what you have here. You need to be away from the edges, for one thing. Take a look at the field from a solenoid and compare it to the field from a current loop--your setup is partway between loop and solenoid.
     
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