Measuring high voltages

The simplest way to get at least a rough value of tension is to measure the maximum distance the voltage can arc over. Just move the electrodes closer together until a spark jumps across the gap. Apart from the voltage, the distance depends mainly on the shape and size of the electrodes and the pressure and kind of surrounding gas. The following tables convert max. distances into approx. volts (peak) for metal balls of the given size in air at normal pressure.

1 cm radius = 2cm diameter
max. dist. / mm tension / volts
0.5 2900
1 4700
3 11400
6 20400
10 30800
15 39300
20 47000
30 57000
40 64000
50 69000
25cm radius = 50cm diameter
max. dist. / mm tension / kV
51 100
106 200
171 300
257 400

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Jochen Kronjaeger
Kronjaeg@stud-mailer.uni-marburg.de