Particle flux density

The particle  current density j denotes the number  N of particles (e.g. atoms , molecules , quasiparticles ) that move through an area  A in the time interval dt

${\displaystyle j={\frac {1}{A}}\ {\frac {\mathrm {d} N}{\mathrm {d} t}}.}$

The particle flow  I is included

${\displaystyle I={\frac {\mathrm {d} N}{\mathrm {d} t}}}$.

The cause of the movement can be diffusion , as in Fick's law . In the case of electrical conduction , in which the electrons move through the surface in both directions, but a net share flows in one direction, there remains a drift with which the electrons move through the surface.

The particle flux density can also be defined as the product of the particle density and the speed of the particles, ${\displaystyle n}$ ${\displaystyle v}$

${\displaystyle {\vec {j}}=n\,{\vec {v}}}$

where is the mean speed (e.g. the drift speed ) of the particles. The above scalar expression is then obtained by integrating over the area . The scalar product between and the normal component of the surface element ( ) is taken at each point : ${\displaystyle {\vec {v}}}$ ${\displaystyle A}$ ${\displaystyle {\vec {j}}}$ ${\displaystyle \mathrm {d} {\vec {A}}}$

${\displaystyle I=\int _{A}{\vec {j}}\cdot \mathrm {d} {\vec {A}}.}$

See also

• Current density

Web links

• Jürgen Schatz, Robert Tammer: Chemistry and Physics for Physicians .
• Particle flux density , University of Graz.