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Homework Help: Need help with taveling wave sketching

  1. May 7, 2004 #1
    hi everyone,
    i am stuck working on this problem and thought i'd post it to the forum

    if an electric field wave is given by E = 50cos(10^8*t + k*z)

    what does the wave look like at t=0, T/4, T/2 and T (T is period)

    i know that w = 10^8 here and that k = w/2Pi

    i'm killing myself trying to graph this wave at those points in time. please help!! :confused: :confused:
     
  2. jcsd
  3. May 7, 2004 #2

    Gokul43201

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    Actually, k = w/c, c = 3 X 10^8.
    And w/2Pi =1/T or T = 2Pi/w .

    k is a wave-vector or an inverse wavelegth. w is a frequency or inverse time. Their dimensions are completely different.
     
  4. May 7, 2004 #3
    yes you're right. that's what i have written. k = 1/3 (w/c)

    to graph do i just plug in 2Pi/w (or multiple of) for t and 1/3 for k?
     
  5. May 8, 2004 #4

    Gokul43201

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    You have

    E = 50 cos (wt - kz), where w = 2Pi/T, k = w/c = 1/3

    So E = 50 cos (2Pi*(t/T) - z/3)

    You are given different values for t/T, ie. 0, 1/4, 1/2, 1. If you plug these in you get E vs. z
     
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