1. Limited time only! Sign up for a free 30min personal 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!

Homework Help: Solving for 3dB frequency appproximations

  1. Aug 4, 2013 #1
    1. The problem statement, all variables and given/known data

    I have the transfer function:

    F(s) = s^3 / ((s+12)(s+550)(s+680))

    Find the lower cutoff frequency (3dB point)

    2. Relevant equations

    s = jw

    3. The attempt at a solution

    I set the equation equal to 1/sqrt(2), use s = jw, and try to solve for the frequency. Now I'm just supposed to "Put it into your calculator and off I go", but what exactly do I put into my calculator? I have a Ti-84, is that able to solve these types of problems?

    What's throwing me off is the imaginary term 'j', I'm not exactly sure what to do with it when solving this polynomial.
  2. jcsd
  3. Aug 4, 2013 #2

    rude man

    User Avatar
    Homework Helper
    Gold Member

    You need to find the magnitude of a complex number.

    It's |a + jb| = sqrt(a^2 + b^2).

    So find a and b for your transfer function and set the magnitude = 1/sqrt(2).
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted