Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Frequency Response Dilemma

  1. Mar 2, 2008 #1
    1. The problem statement, all variables and given/known data

    This is related to the frequency response topic.
    Given transfer function G(s) = 4/(s+1)
    and input is sinusoidal i.e. 2 sin (10t + 10)

    2. Relevant equations


    3. The attempt at a solution

    I have found out that the magnitude of the transfer function G(s) is 4/sqrt(101) with phase angle -84 degree.

    Is the output
    (4/sqrt(101) + 2) sin (10t - 74) ?
    because that is what i was told.

    All these while I thought that the magnitude of G(s) have to be multiplied with the magnitude of the input sinusoidal to obtain the magnitude of the output. But in this case, he just add both of them together.
    Please clarify. =)
  2. jcsd
  3. Mar 2, 2008 #2


    User Avatar

    First of all the 10 in sin(10t + 10) is radians, so you can not add it to -84 degree and obtain 74 radians.
    And yes, the gain of the transfer function must be multiplied by and not summed to the amplitude.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook