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Finding frequency of an AC current sin wave?

  1. Apr 19, 2017 #1
    1. The problem statement, all variables and given/known data
    An AC current is given by I= 475 sin( 9.43 t), with I in milliamperes and t in milliseconds. Find the frequency.

    2. Relevant equations
    w = 2pi*f

    3. The attempt at a solution
    I got 9.43/2pi which is 1.5 Hz, but that is wrong. I honestly have no idea what to do to find the Hz.
     
  2. jcsd
  3. Apr 19, 2017 #2

    gneill

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    Staff: Mentor

    Pay close attention to the units specified :wink:
     
  4. Apr 19, 2017 #3
    Would I convert milliamperes to amperes and get 0.001501 instead of 1.5? Also the only units are millamperes and frequency is in Hertz which is cycles per second.
     
  5. Apr 19, 2017 #4

    gneill

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    Staff: Mentor

    The current units are inconsequential. They don't affect frequency. However:

    is important.
     
  6. Apr 19, 2017 #5
    The 9.23t is in milliseconds correct? Hertz is in seconds though so instead of 9.23 it would be 0.00923 s correct? So I would get 0.00923/2pi = 0.001501 Hz.
     
  7. Apr 19, 2017 #6

    gneill

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    Staff: Mentor

    No, you've gone the wrong way with the scaling.

    Think of it this way: If t is in milliseconds, then after 1 millisecond the argument of the sine function should give 9.43 radians. That is, the constant 9.43 is associated with the units: radians/millisecond.
     
  8. Apr 19, 2017 #7
    OHHHHHH so instead it is 9430 rad/s. Ok so the answer should be 1500 Hz. Thanks!!!!
     
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