AC circuit with resistor

Discussion in 'Homework Help' started by logearav, Oct 4, 2011.

  1. logearav

    Thread Starter Member

    Aug 19, 2011
    248
    0
    Revered members,
    Please see my attachment, which is an AC circuit with resistor. In such circuit the applied voltage is in phase with current. My doubt is
    1) In Vector diagram, why the amplitude of voltage is greater than current?
    2) Similarly in phasor diagram, the length of Voltage is greater than the length of current. Why?
     
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
    5,448
    782
    It's simply an arbitrary assignment by the author. Comparing the relative voltage and current magnitudes is meaningless. One can only compare 'like with like' in matters of physical quantities - voltage with voltage and current with current.

    If the author had shown the scale of the current to be greater than the voltage you would have been asking virtually the same question.
     
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  3. Maen

    Member

    Sep 16, 2011
    12
    4
    1 ) You have to conssider ohm's law : \vec{U} = \vec{Z} \cdot \vec{I}
    so you have a factor \vec{Z} = R between voltage and current. If R = 1 \Omega then current and voltage would have the same amplitude.
    2) Time diagram and phasor diagram basicaly display the same information. So they better display the same values ;)
     
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  4. wmodavis

    Well-Known Member

    Oct 23, 2010
    737
    150
    V is a independant variable and I a dependant variable - i.e. as Maen says it is dependant on R. Change R and you can theoretically make the vector I be any length you want. How long do you want it to be?
     
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  5. logearav

    Thread Starter Member

    Aug 19, 2011
    248
    0
    Thank you all, for the replies. So, there is no harm if i draw Voltage and Current, with same length and also with same amplitude. Am i right?
     
  6. Maen

    Member

    Sep 16, 2011
    12
    4
    Actually current and voltage not beeing on the same scale (Ampers resp. Volts) you can display it however you want, just adapt your scales to fit ;). But it's not uncommon to represent the current smaller than the voltage since the current's numerical value is usually smaller. But not doing so is in no way incorrect.
     
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