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Original poster: "Kurt Schraner" <k.schraner@xxxxxxxxxxx>

Hi all,

it was a certain surprise, when we noticed, that swiching a powerful induction coil with it's ~50kV HV side connected to a Jacobsladder, was developping enough E-field force, to set the wires of a resting JL in slight mechanical movement, _before_ a spark occured. Each of the 2 wires of the JL may be viewed as a leaf-spring-mounted-in-a-vice system, with it's characteristic mechanical fundamental resonant frequency.

In the following movie-clip my coiler-friend is periodically switching the Andiruptor on and off, in order to set it in mechanical oscillation with growing amplitude (~analogue to initiating a swing for children). But first watch this ~3MB movie:


...I assume, the movie has already made you understand what happened: Andi amplifies the (mech.)amplitude of the JL, till a spark at the upper end shows up. Now he can stop switching the induction coil periodically (hear the sound!), because the oscillation continues by itself!!! The spark shortcuts the wires, collapsing thereby the E-field to almost zero, and the electrostatic attraction between the wires ceases. The wires swing to max.distance, the spark extinguishes, and the force reappears, attracting the wires... etc., etc. --> we have our "Jacobsladder-oscillator" ;-) It can be noticed from the movie, the JL being at rest in the start, and never be moved by any means before starting the switching of the Andiruptor (watch Andi's hand). The JL itself is made of 2 massive copper wires of 8mm diameter and about 1.8m length. This leads to a low mechanical Eigenresonant frequency. The electrostatic force between the wires is estimated to about 0.1-1N, when applying about 50kV HV. The following ~1.1MB movie shows the JL in it's _normal_ use:


We have observed: the higher the frequency of the HV applied to the JL, the slower the spark is moving upwards (the Andiruptor allows going up to the kHz range).

We consider the "JL-oscillator" a pretty and simple demonstration of electrostatic force, and count our experiment -at least currently- to our favorites :-)