Can there be an resonance in LR circuit?

Discussion in 'Homework Help' started by Tera-Scale, Jan 2, 2011.

  1. Tera-Scale

    Thread Starter Active Member

    Jan 1, 2011
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    Why am I asked to find the frequancy at which an LR circuit is resonant? Every formula that I saw always included a negative reactance for a capacitor in series.
     
  2. edgetrigger

    Member

    Dec 19, 2010
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    There is no resonance without C. There shoul be something missing in the question. LR can be used as a filter at the most.
     
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  3. Tera-Scale

    Thread Starter Active Member

    Jan 1, 2011
    164
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    Thanks, I would assume it's a mistake in my assignment.. :/
     
  4. Papabravo

    Expert

    Feb 24, 2006
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    Resonance can only occur in a second order system. The series RL circuit is a first order system.
     
  5. hobbyist

    Distinguished Member

    Aug 10, 2008
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    As already mentioned no resonance, but the question may be asking,
    "at what frequency, does (XL = R), such as used in filter branches.
     
  6. mik3

    Senior Member

    Feb 4, 2008
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    Maybe the question refers to parasitic capacitance which resonates with the inductance.
     
  7. edgetrigger

    Member

    Dec 19, 2010
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    if we were to consider stray capacitance then it will be an LC and still not an LR resonance.
     
  8. Papabravo

    Expert

    Feb 24, 2006
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    A series LR circuit is an idealization, without capacitance, and thus incapable of resonance. Now it is true that in a real circuit as you increase the applied frequency you reach a point where there is a small capacitance between the individual windings of the inductor whose reactance becomes significant. Now it is no longer an RL circuit and we can get resonance.
     
  9. edgetrigger

    Member

    Dec 19, 2010
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    Even then it is a LC resonace and not a RL resonance.
     
  10. Papabravo

    Expert

    Feb 24, 2006
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    Of course. That is what we have been trying to say. There is no such thing as either an RL resonance or an RC resonance. You need BOTH an L and a C for rsonance to occur.
     
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