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# Townsend (unit)

The Townsend (symbol Td) is a physical unit of E / N, where E is electric field and N is concentration of neutral particles. It is defined by the relation $1 {\rm Td} = 10^{-17}\rm V\cdot cm^2$.

### Additional recommended knowledge

This unit is important in gas discharge physics, because the mean energy of electrons (and therefore many other properties of discharge) is a function of E / N. It means that increasing the electric intensity E by some factor q has the same consequences as lowering gas density N by factor q.

It is named after John Sealy Townsend (see other articles in this stub).

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Townsend_(unit)". A list of authors is available in Wikipedia.
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