1. Not finding help here? Sign up for a free 30min 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!

RMS of square wave and alternating currents

  1. Sep 25, 2016 #1
    1. The problem statement, all variables and given/known data
    Find the value of the RMS current in the following cases:
    (a) a sinusoidally varying curent with a peak value of 4.0 A,
    (b) a square wave current which has a constant value of 4.0 A for the first 3 ms and -2.4 A for the next 2 ms of each 5 ms cycle,
    (c) an alternating current which has the same effect as a steady DC current of 2.4 A,
    (d) a 240 V RMS supply driving current through a 16 Ω resistor.

    Answers: (a) 2.8 A, (b) 3.3 A, (c) 2.4 A, (d), 15 A

    2. The attempt at a solution
    (a) I = I0 / √2 = 4 / √2 = 2.8 A

    (b) Average value of I2 = 42 + 42 + 42 + (-2.4)2 + (-2.4)2 / 5 = 11.904 → RMS = √11.9 = 3.45 A. Did I miss something? I would say a difference of 0.15 / 0.2 is relatively significant, though I don't see any mistakes.

    (c) An alternating current which has a same effect as a steady DC current of 2.4 A has an RMS value of 2.4 A.

    (d) V = IR → I = V / R = 240 / 16 = 15 A

    Are (b) and (c) right? Did I miss something or it's just a typo in (b)?
     
  2. jcsd
  3. Sep 25, 2016 #2

    gneill

    User Avatar

    Staff: Mentor

    Your 3.45 A for (b) looks good.
     
  4. Sep 25, 2016 #3
    So it's probably a typo in the book?

    And (c) logic is correct?
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: RMS of square wave and alternating currents
  1. Rms current (Replies: 3)

Loading...