Example question

Discussion in 'Homework Help' started by jaymo3141, Feb 21, 2014.

  1. jaymo3141

    Thread Starter New Member

    Feb 16, 2014
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    Can someone explain why i1 doesn't lead i3 by 345 degrees?
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    3,353
    Try drawing the three currents as vectors on a polar plot.
     
  3. WBahn

    Moderator

    Mar 31, 2012
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    First, get all three into the same form, namely

    i_n(t) = I_N cos(ωt + θ_n)

    Then determining how much one leads another becomes trivial.
     
  4. screen1988

    Member

    Mar 7, 2013
    310
    3
    In i_n(t) = I_N sin(ωt + θ_n) what is the range of θ_n?

    -180 degrees to 180 degrees or 0 to 360 degrees?
    I got two different results with the question i1(t) leads i3(t).
    If θ_n is from -180 to 180 degrees then i1(t) leads i3(t) by 165 degrees.
    If θ_n is from 0 to 360 degrees then i1(t) leads i3(t) by -195 degrees.
     
    Last edited: Feb 21, 2014
  5. WBahn

    Moderator

    Mar 31, 2012
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    It shouldn't matter what range you choose. Either way, you may need to normalize the answer, but the answers should be the same modulo 360°.
     
    screen1988 likes this.
  6. screen1988

    Member

    Mar 7, 2013
    310
    3
    I realise I made a mistake. The first case is 165 degrees and the second is -195 degrees.
    And as you said both are correct. There is an infinite number of the correct answers here?
     
  7. WBahn

    Moderator

    Mar 31, 2012
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    Yes, though common practice is to reduce it to less than one complete revolution in either direction and to normally restrict even that to a total range of just one revolution overall.
     
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