1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Freq response of forced sinusoidal motion:

  1. Nov 28, 2009 #1
    The book I am currently reading derives the response of an electron to an applied sinusoidal field as:

    1/[1 + 2i (w - wa)/g] = 1 / (1 + i delta)

    where w and wa are the induced and resonance response frequencies and g the damping constant.

    And delta = 2 (w - wa)/g

    Up to this point there is no problem. But the book then states that the amplitude squared or power response has the form:

    1/[1 + {2 (w - wa)/g}2 ] = 1 / (1 + delta2)

    And here is the problem.... if you square the first equations listed you don't get what they give as the power response. I think the answer should be:

    1 / (1 + 2 i delta - delta2)

    Is there some assumption I am missing, its not just the imaginary term is missing the sign is wrong for the squared term??

    Thanks for any help!
     
  2. jcsd
  3. Nov 28, 2009 #2

    Redbelly98

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    For complex amplitudes, one squares the absolute value of the amplitude to get the power response.
     
  4. Nov 30, 2009 #3
    :redface: Thanks!
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook