Help with Phase Angle calculation

Discussion in 'Math' started by kevinaussie, Jan 26, 2009.

  1. kevinaussie

    Thread Starter New Member

    Jan 26, 2009
    1
    0
    I am doing a practice Test.

    The question is what is the Phase angle between the V and I
    XL=27.2 and R= 20
    Phase angle = arctan (XL/R)
    arctan(27.2/20)

    what is the answer?
    I get arctan(1.36)
    or 53.67
    that is the wrong answer on my test!

    Thanks Kevin
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    The correct answer is -53.67 because the current lags the voltage (if you take voltage with an angle of 0).
     
  3. ayaprad

    New Member

    Dec 23, 2008
    1
    0
    u did not mention the voltage is taken across what R or L?

    if its R, then the ans is -58 as mik said. or if its across L, then the answer is 90-58. if its across both R,L then the answer is 0.
     
  4. dig1

    Member

    Jul 31, 2008
    18
    0
    i am intrigued by this explanation... can somebody please lay out the fundamental equation for why this is a negative number,.... thanks
     
  5. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    If you take the voltage wave form as the reference (ie 0 phase angle) then if the current lags the voltage (case of inductive load) the current will be delayed some degrees. Thus, the current reaches its peak value after a while the voltage does and and this suggests a negative angle with respect to the voltage.
     
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