### 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
`