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Wavelength dependence of a resonant coil?

  1. Jun 28, 2010 #1
    This question relates to the design of a Tesla coil, which is basically a loose-coupled, tuned transformer.
    The secondary is a series LCR circuit that develops a high voltage across a capacitor. The capacitor takes the form of a toroidal 'top-load' to ground.

    In the literature, much importance is given to the length of the wire used in constructing the coil: stating that it must be 1/4 wavelength for the design frequency.
    Tesla himself made this statement - and he must have been fully aware of Maxwell's Equations.

    I can't reconcile that statement with my understanding of the physics of inductance and resonance.

    At resonance, the impedance of the coil and capacitor are equal and opposite in phase, the result is a minimum in total impedance - it becomes equal to the DC resistance. The resulting high current develops a voltage across the impedance of the capacitor.

    I am aware that the inductance of a coil is influenced by the wavelength as a secondary effect that is important in RF work but that would only result in a (small) shift of resonant frequency, whereas the claim is for huge amplification of the resultant voltage.

    I'm willing to believe there may be some other effect (maybe reduced losses due to corona discharge in the coil).

    Any ideas/comments anyone?
  2. jcsd
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