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Wimshurst

Wimshurst charged Leyden jars discharged through a wire loop


Wimshurst electrostatic generator with a wire loop for discharge.  RF from two cases were observed - one using a 2-meter loop and another using a 4-meter loop.  The picture shows the Wimshurst generator and a spark from one Leyden jar ball electrode and one end of the discharge loop.  The other end of the discharge loop is in direct contact with the ball electrode of the second Leyden jar. The spark duration is about 2 usec (as determined using a fast photodiode).  We estimate that the collective capacitance of the Leyden jars is about 200pf.

Detected RF - 4 meter case


Discharge of Wimshurst Leyden jars through a 4-meter loop.  O-scope channel is connected to short wire that serves as an antenna.  Spark is nominally 2 usec in duration as determined by a separate test.  Observed frequency is about 6 MHz.

Detected RF - 2 meter case


Discharge of Wimshurst Leyden jars through a 2-meter loop.  O-scope channel is connected to short wire that serves as an antenna.  Spark is nominally 2 usec in duration as determined by a separate test.  Note that the oscillation frequency is higher in this case relative to the 4-meter loop case.  Since the loop length is half of the previous case, one expects the frequency to be higher by sqrt(2).  Observed frequency here is about 10 MHz, which is a little bit higher than the 8.4 MHz value (1.404 times 6 MHz), that one might expect.

Time history: Spark light and RF


These oscilloscope traces are for discharge of Leyden jar through the 2-meter-long wire loop. The upper trace records a time history of the light from the spark - it was as recorded using a back-biased SGD-040L photodiode into a 1000-Ohm load.  A 4-inch diam., 6-inch f.l. lens was used to collect the light.  The lower trace is RF as picked up using a short antenna.  To get a clean signal on the upper trace, it was necessary to build a Faraday shield (using aluminum foil) around the Wimshurst machine, Leyden jars, and wire loop.

Size: 17.5M bytes Modified: 13 June 2013, 08:02