# Mobility

From AMS Glossary

## mobility

Quantitative measure of the velocity of ions in an electric field of unit strength.

The mobility can be expressed as where

*v*is the velocity of the ion and*E*is the electric field strength. The units are square meters per volt per second. Heavier ions will have lower mobilities than lighter ones and values of mobility vary inversely with density, producing slower mobilities near the earth's surface.