Quick instantaneous sin value question

Discussion in 'Homework Help' started by markp912, Mar 6, 2009.

  1. markp912

    Thread Starter Member

    Feb 4, 2009
    14
    0
    Q: A certain sin wave has a positive going zero crossing at 0° and an rms value of 20V. Calculate its instantaneous value at each of the following angles: (a)15° (b)33° (c)325°

    So my Vp=28.28
    But since my starting point is at 0° would that mean each of those angles are lagging and i would have to use the formula: y=Vp sin(θ-Φ)?

    Or would i just use y=Vpsinθ

    Thank you.
     
  2. RiJoRI

    Well-Known Member

    Aug 15, 2007
    536
    26
    WHY are they lagging? Lagging in regard to what? And why couldn't you return the values as RMS?

    Methinks thou art working too hard!

    --Rich
     
  3. markp912

    Thread Starter Member

    Feb 4, 2009
    14
    0
    lagging b/c the new angle is at 30° now?
     
  4. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    Your minimum voltage is at 0 deg, and the maximum is at 90 deg. Why worry about lead/lag?
     
  5. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    RMS has no meaning for instantaneous voltage readings.
     
  6. markp912

    Thread Starter Member

    Feb 4, 2009
    14
    0
    Wouldnt the 325° angle lag b its so far out from 0°?
     
  7. Ron H

    AAC Fanatic!

    Apr 14, 2005
    7,050
    657
    Would a picture help?
     
  8. markp912

    Thread Starter Member

    Feb 4, 2009
    14
    0
    WOW! that picture did help a lot. i feel like an idiot now. there is only one sine wave going. thanks for all of your help guys.
     
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