It has been observed that in case of very small gaps of less than a mm and the gas pressure between the gap lies in the range 10–9 to 10–2 torr, there is no change in the breakdown voltage i.e, if the gap length is small a variation of gas pressure in the range given above doesn’t affect the breakdown voltage.
However, if the gap length is large say about 20 cm, the variation of gas pressure between the gap adversely affects the withstand voltage and the withstand voltage lowers drastically.
