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Homework Help: Leading and Lagging voltages

  1. Mar 20, 2012 #1
    This is just an example

    X has to be positive so X=-20cos(t±180deg)
    I know you want the angle ^ to be the smallest magnitude, but for this case both would give you a magnitude of 180 deg.
    So which one would you pick X=20cos(t-180deg) or X=20cos(t+180deg)?
    This would change the answer of whether X or Y was leading.

    Someone told me you should pick the angle that makes a phase difference that is <180deg.
    So in this case it would be X=20cos(t-180deg) since that would give a phase difference of 135 degree compared to the 180+45=225deg phase difference if we picked the positive.

    Is that right?
    Last edited: Mar 21, 2012
  2. jcsd
  3. Mar 20, 2012 #2


    X leading normal sine wave Z by 90 degree
    Y lagging normal sine wave Z by 45 degree.

    X leading Y by 135 degree.
    http://img855.imageshack.us/img855/5074/leadlag.jpg [Broken]
    Last edited by a moderator: May 5, 2017
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