# Homework Help: Calculate phase between sine waves given the time difference

1. Sep 4, 2009

### exidez

1. The problem statement, all variables and given/known data

How do i find the phase between sine waves knowing the time difference between each?
http://users.bigpond.net.au/exidez/sinewave.jpg

Equation for the main function is 3cos(30t - Pi/2)
The smaller sine wave is of the same frequency when is settles in a steady state.

2. Relevant equations

i thought it was
time difference * 2*Pi*f = phase difference in radians

3. The attempt at a solution
30 = 2*Pi * f

-1.5*360/(2Pi) = -85.94 degrees

MATLAB give the phase difference as -76.3995 degrees
this is equivalent to -0.0444474274 difference in seconds

Is this just due to rounding error??

Last edited by a moderator: Apr 24, 2017
2. Sep 4, 2009

### exidez

i think i just answered my own question... 2.57 seconds for the larger sine wave still give an amplitude of 3.. In this case the time difference is -0.04.

it definitely is due to rounding

3. Sep 4, 2009

### Redbelly98

Staff Emeritus
You did it right, but note that the 0.05s time difference contains just one significant figure.