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Convert waveform formula to 'usual' cos sin formula to sketch graph

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Discussion in 'Electronics Homework Help' started by Ian Wright, Nov 21, 2017.

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  1. Nov 21, 2017 #1
    Ian Wright

    Ian Wright

    6
    0
    Nov 21, 2017
    Hi.
    I am used to drawing cos sin waves graphs from formulas that look like:

    Y = A cos (B (x-c) ) + D
    where A = amplitude, B = Period (2pie / B), C= Horizontal Phase Shift, D=Vertical Shift.

    But I have the formula Vt = 10cos (650t + 0.0015) and cannot understand how it relates to the formula's I am used to? Does anyone have any ideas of where I get the period and phase shifts from it?
    Many Thanks
     
  2. Nov 21, 2017 #2
    Harald Kapp

    Harald Kapp Moderator Moderator

    10,806
    2,437
    Nov 17, 2011
    Maybe look like but are the same as. Have a closer look at this equation:

    This should be
    Y = A cos (B*x-c) ) + D as the phase shift c is fixed and not time variable. The time variable part would be the frequency (or equivalent to the inverse of the period).
    Then the correspondence is obvious.

    This makes no sense as B = 2*Pi/B means B is fixed at B = sqrt(2*Pi). The period of a sine is defined as 1/f where f is the frequency in Hz.
     
  3. Nov 21, 2017 #3
    dorke

    dorke

    2,342
    665
    Jun 20, 2015
    This may help you (from wiki):

    sine.jpg

    There is no "D=Vertical Shift" here,but it can be easily added if needed.
    We call it the "DC part", i.e zero frequency part.
     
  4. Nov 22, 2017 #4
    Ratch

    Ratch

    1,088
    331
    Mar 10, 2013
    I don't see what the problem is. Simply convert the coefficient 650 into a frequency as shown below.
    Wright1.JPG
    Below is plot of the original equation.
    Wright2.JPG
    And, it matches with the revised equation.
    Wright3.JPG
    Ask if you have any questions.

    Ratch
     
  5. Nov 22, 2017 #5
    Harald Kapp

    Harald Kapp Moderator Moderator

    10,806
    2,437
    Nov 17, 2011
    Have a close look at the way the parentheses are set. The equation as posted by the op makes not much sense.
     
  6. Nov 22, 2017 #6
    Ratch

    Ratch

    1,088
    331
    Mar 10, 2013
    True, it is a clunky, clumsy way to present a simple trig equation. But, I was trying to show him how to find the frequency and period of the second equation involving the 650 times "t" term. I let him figure out how to simplify the phase change term of 10.

    Ratch
     
  7. Nov 22, 2017 #7
    Ian Wright

    Ian Wright

    6
    0
    Nov 21, 2017
    thanks so much guys, think I've got it now. Much appreciated.
     
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