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Homework Help: Current across resistor and inductor

  1. May 2, 2007 #1
    1. The problem statement, all variables and given/known data
    I have a resistor and an inductor in series. The current across each is the same, correct? I want to know if I can use Ohm's Law to solve for current across the inductor if I know the Voltage and inductive reactance. Basically, does I = V/X_{L} ?

    2. Relevant equations

    V = IR
    I = V/R

    does I = V/ X_{L} ?

    3. The attempt at a solution
  2. jcsd
  3. May 2, 2007 #2


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    Science Advisor

    ??What do you mean by X_{L}? I can guess that V is the voltage drop, I the current and R the resistance. Is X_{L} the inductance? If so then, no, the voltage drop over an inductance is NOT given by the same equation as for a resistance. Surely you have that formula in your text?
  4. May 2, 2007 #3

    by this i mean inductive reactance...sorry, it's tex syntax for X with L as a subscript. i have the habit of writing all my mathy stuff in latex syntax
  5. May 2, 2007 #4


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    Yes, [tex]I = \frac{V_L}{X_L}[/tex]
    Notice that [tex]X_L[/tex] is dependent of the frequency of [tex]V_L[/tex]
  6. Feb 21, 2009 #5
    Forget the problem for a minute, first lets clear up that current isn't across anything. Current flows through and voltage is established across. Like fingers on a chalk board.:cry:
  7. Feb 21, 2009 #6
    If those 2 elements are in series (the resistor and inductor) and connected to a voltage source, the current through all elements will be given by:

    I = VS / (R + XL)

    If the voltage you are talking about is the voltage across the inductor, then yes, the current through all elements will given by:

    I = VL / XL
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