adding complex angles

Discussion in 'Homework Help' started by Hawkeye87, Nov 4, 2008.

  1. Hawkeye87

    Thread Starter Active Member

    Oct 7, 2008
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  2. scubasteve_911

    Senior Member

    Dec 27, 2007
    1,202
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    In this case you can use use c^2=a^2 + b^2 for the magnitude of the resultant vector, then use any trig identity to solve for the angle.

    theta = arctan(8/6)
     
  3. Ratch

    New Member

    Mar 20, 2007
    1,068
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    Hawkeye87,

    Although the reference you cited talks about vectors, voltage is not a vector quantity. It has magnitide but not direction. Alternating voltages can be represented by phasors, which have magnitude and an angular relationship between them. Phasors also have some vector like properties, but not all of them. To add voltage phasors, split up each into real and orthogonal parts. Add up the real parts and the orthogonal parts. Then convert back to polar form if desired, or leave it like it is. scubasteve_911 touched on how to convert to polar form.

    Ratch
     
  4. Hawkeye87

    Thread Starter Active Member

    Oct 7, 2008
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    I figured out that question and i now have yet another....
    If
    V1 = 80sin(ωt + 25°)
    V2 = 10sin(ωt - 15°)
    find the sum Vt=V1+V2 where the angular velocity (ω) is 400.
    Where do you start?
     
  5. Ratch

    New Member

    Mar 20, 2007
    1,068
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    Hawkeye87,

    Angular velocity is irrelevant, so long as it is the same for both voltages.

    80/_25 = 72.50 +j33.81
    10/_-15 = 9.66 +j-2.59

    72.50+9.66 + j33.81-j2.59 = 82.16 + j31.22 = 87.90/_20.81

    Ratch
     
  6. Hawkeye87

    Thread Starter Active Member

    Oct 7, 2008
    52
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    now how would i calculate the frequency, period, peak to peak voltage of V1, the rms voltage of V2, the phase difference between V1 and V1 and the time difference between the two. Just set me up the equations and i'll have at it.
     
  7. Ratch

    New Member

    Mar 20, 2007
    1,068
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    Hawkeye87,

    2*Pi*f = w = 400

    P = 1/f

    You have to specify what the voltages given were.

    25 degrees - 15 degrees = 10 degrees

    (10/360)*P

    I feel so guilty and ashamed for "helping" you so much. You will probably flunk out unless you can do problems like this yourself.

    Ratch
     
  8. Hawkeye87

    Thread Starter Active Member

    Oct 7, 2008
    52
    0
    don't feel guilty. your helping someone who has a test friday that knows maybe half this. So consider the fact that your aiding my learning process by filling in the gaps that the teacher leaves out.
     
  9. The Electrician

    AAC Fanatic!

    Oct 9, 2007
    2,281
    326
    Ratch, do you see anything wrong with the first paragraph on this page:

    http://en.wikipedia.org/wiki/Phasor

     
    Last edited by a moderator: Nov 5, 2008
  10. Ratch

    New Member

    Mar 20, 2007
    1,068
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    The Electrician,

    No, I don't. But that is not the page that Hawkeye87 referenced.

    Ratch
     
  11. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
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    Back on topic, if you please, gentlemen. Let's help the O.P. with complex numbers, not argue about semantics.

    Ratch: if you have a problem with the AAC website, make your comment in the appropriate forum - this one is for helping folk with homework.
     
  12. Ratch

    New Member

    Mar 20, 2007
    1,068
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    thingmaker3,

    I did help the OP, perhaps more that I should have. It is not a matter of semantics, it is about facts. Voltage is not a vector quantity.

    I did not dwell on the mistake in the AAC, just a quick remark to get the OP on the right track. Which was helping him with his homework.

    Ratch
     
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