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: Basic Phasor addition

  1. Oct 3, 2011 #1
    1. The problem statement, all variables and given/known data

    If I have three different waves each with difference amplitude and phase angle how would i find the combined phase angle shift?

    wave 1: A=5 phi=0
    wave 2: A=5 phi=pi/4
    wave 3: A=9 phi=pi/2

    2. Relevant equations

    phi'=arctan(a2sin(phi)/(a1+a2cos(phi)), where phi in this case is the difference between the phase angles of two waves.

    3. The attempt at a solution

    My first strategy was to add wave 1 and 2 and then add their sum to wave three. this gave me the correct combined amplitude of 15.29. I then applied the same thinking to the phase angles but the answer i got was incorrect so i tried vector addition and using the law of cosines and I got a nonsensical answer - arcos(-1.41). Needless to say i need a nudge in the right direction. Thanks for the help
  2. jcsd
  3. Oct 3, 2011 #2


    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    Think of the (A,Φ) values as polar coordinates of vectors. Convert them to (x,y) coordinates, and then it's standard vector addition from there.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook