Paschen's Law, also known as Paschen's curve or Paschen's breakdown law, is a fundamental principle in the field of electrical engineering and plasma physics that describes the breakdown voltage of a gas between two electrodes at a given pressure as a function of the gap distance between the electrodes. In simpler terms, it explains the voltage required to initiate electrical discharge (ionization) in a gas-filled gap between two electrodes.
The law is named after Friedrich Paschen, a German physicist who conducted experiments in the late 19th century to study the behavior of electrical breakdown in gases. Paschen's Law is particularly important for understanding the behavior of gases at low pressures, such as those found in vacuum tubes, gas discharge lamps, and certain industrial applications.
The general form of Paschen's Law can be expressed as:
=
โ
โ
ln
โก
(
โ
+
ln
(
B
)
)
V=Bโ
ln(
pd+ln(B)
Aโ
d
โ
)
pโ
d
โ
Where:
V is the breakdown voltage between the electrodes.
p is the gas pressure.
d is the distance between the electrodes.
A and
B are constants that depend on the properties of the gas and the electrodes.
Paschen's Law indicates that there is an optimal pressure for achieving breakdown at a given electrode distance. At very low pressures, the breakdown voltage is relatively high due to the scarcity of gas particles available for ionization. As the pressure increases, more gas particles become available for ionization, and the breakdown voltage decreases. However, at very high pressures, the breakdown voltage tends to increase again due to the greater density of gas molecules, which can hinder the movement of charged particles.
In summary, Paschen's Law provides valuable insights into the conditions under which electrical breakdown occurs in gases, and it is essential for designing and operating various devices and systems that involve gas discharges, such as neon signs, fluorescent lamps, and certain types of electrical insulation.