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Homework Help: It's me again. need somebody to check my answer

  1. Apr 7, 2004 #1
    Hi all,

    it's me again... sorry but this is the only place where I learn most of my physics from... pls kindly check my answer and for the last part... I found the angle but don't know how to convert it to (rad)... pls guide me...thanks

    A series RCL circuit with L= 6.5 mH, C=3.7uF, and R = 5.5ohm is driven by a generator with a maximum emf of 197 V and a variable angular frequency w.

    (a) Find the resonant frequency . (Unit: rad/s)

    6.45E3 rad/s

    (b) Find I(rms) at resonance when w=7.0E3 rad/s . (Unit: A)

    25.3 A

    (c) Find X(c) when w=7.0E3 rad/s. (Unit: ohm)

    38.6 ohm

    (d) Find X(L) when w=7.0E3 rad/s. (Unit: ohm)

    45.5 ohm

    (e) Find Z when w=7.0E3 rad/s. (Unit: ohm)

    8.82 phm

    (f) Find I(rms) when w=7.0E3 rad/s. (Unit: A)

    15.8 A

    (g) Find the phase angle when w=7.0E3 rad/s. (Unit: rad)

    phase angle = inverse tan ((45.5-38.6) / 5.5) = 51.4

    answer: I found the angle to be 51.4 degrees but how do I convert it to unit - rad?

    thanks
    cseet
     
  2. jcsd
  3. Apr 7, 2004 #2
    If I'm not mistaken this is a conversion between degrees and radians.

    [tex]\frac{2 \pi}{360} = \frac{x}{51.4}[/tex]

    and solve for x. Don't factor out [tex]\pi[/tex], use it in your answer. For example [tex]x = 0.98 \pi[/tex]
     
    Last edited: Apr 7, 2004
  4. Apr 7, 2004 #3
    All answers are correct (good job!) except for (b) which I cannot confirm nor deny. I still don't understand the meaning of "I(rms) at resonance when w=7.0E3 rad/s" when the only resonance frequency is 6.45E3 rad/s. If they only want you to find I(rms) at w=7.0E3 rad/s, then the answer should be the same as (f), 15.8A.
     
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