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Polar form of phasor

  1. Apr 15, 2015 #1
    Hello

    Excuse me, but how do I sketch the phasor of a voltage that it's V=5cos(10t+30degrees) and how the V=5sin(10t+30degrees) ?

    I know that these can be converted as the R<angle polar form, with R being the Vmax, ie the 5, and the angle the phase.

    But what doesn't it matter if I have cos or sin???

    thanks
     
  2. jcsd
  3. Apr 15, 2015 #2
    Cosine is 90 degrees out of phase with sine.
     
  4. Apr 15, 2015 #3

    I know that

    the problem is how do I represent the cos phasors with polar form complex number and how the sin phasors
     
  5. Apr 15, 2015 #4

    SammyS

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    ##\displaystyle e^{i\theta}=\cos(\theta)+i\sin(\theta)##
     
  6. Apr 15, 2015 #5
    I said polar form, not euler
     
  7. Apr 15, 2015 #6

    SammyS

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    It is the basis for polar.

    ##\displaystyle 5\cos(\theta)=\text{Re}\left(5e^{i\theta}\right) ##
     
  8. Apr 15, 2015 #7
    can you forget altogether Euler?
    I only deal with rectangular and polar forms
     
  9. Apr 15, 2015 #8

    SammyS

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    Excuse me.
     
  10. Apr 15, 2015 #9
    I don't know euler

    the question is precise:

    write in polar form: V=Vmaxsin(100t+30) and V=Vmaxcos(100t+30)

    the problem is:
    1) do I write Vmax<30 and Vmax<120 ?
    2) do I write Vmax<-60 and Vmax<30 ?
    something else?
     
  11. Apr 15, 2015 #10

    SammyS

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    (In the green bar at the top of the Text Window: Use the X2 button for subscripts, the X2 button for superscripts. It makes V=Vmaxcos(100t+30) be more readable.

    Click the big and you get to chose from a set of useful technical characters at the bottom of the text window, including ' ∠ ' . )

    In my experience, it's customary to use cosine as the basis, i.e. zero phase, but I have seen sine used on occasion.

    Vmax∠-60 and Vmax∠30 seems likely.
     
  12. Apr 15, 2015 #11
    but aren't these two differest sets of polar form numbers?
    there should be a unique way, they cannot be both valid!
     
  13. Apr 15, 2015 #12

    SammyS

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    It's not written on some great stone tablet that you must use cosine or that you must use sine.

    If some author chooses an unconventional notation, he/she only need be consistent (and hopefully she/he warns the reader).
     
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