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RL circuit inductive reactance problem

  1. May 12, 2013 #1
    1. The problem statement, all variables and given/known data

    There's a coil, resistance R=7Ω, and inductance L=1mH, and its powered by a generator with variable frequency and Vmax=10V.
    At what frequency is inductive reactance equal to resistance? (when z=R√2)

    2. Relevant equations

    z=R√2, z=√(R2+(ωL)2)

    3. The attempt at a solution

    I plugged in z=R√2 to z=√(R2+(ωL)2), and solved for ω. This ends up just simplifying to ω=R/L, which is 7Ω/0.001H, giving 7000Hz. But my teachers answer is 1110Hz. Am I doing something wrong here? Been stuck on this for a while.
  2. jcsd
  3. May 12, 2013 #2


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    Staff: Mentor

    ω has units of radians/second.
  4. May 12, 2013 #3
    Okay...isn't that basically the same thing? Frequency in measured in hertz, which is an inverse second. And also my teachers answer specifically says 1110 Hz
  5. May 12, 2013 #4


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    Staff: Mentor

    What is the equation relating Hz to radians/sec?
  6. May 12, 2013 #5
    ahh. ω=2∏f. my bad...i don't know why i didnt recognize that. thanks!
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