Editing Electron mobility (section)

===Relation to current density===
The drift current density resulting from an electric field can be calculated from the drift velocity. Consider a sample with cross-sectional area A, length l and an electron concentration of n. The current carried by each electron must be <math>-e v_d</math>, so that the total current density due to electrons is given by:
<math display="block">J_e=\frac{I_n}{A} = - e n v_d</math>
Using the expression for <math>v_d</math> gives
<math display="block">J_e = e n\mu_e E</math>
A similar set of equations applies to the holes, (noting that the charge on a hole is positive). Therefore the current density due to holes is given by
<math display="block">J_h =e p \mu_h E</math>
where p is the hole concentration and <math>\mu_h</math> the hole mobility.

The total current density is the sum of the electron and hole components:
<math display="block">J=J_e+J_h=(en\mu_e+ep\mu_h)E</math>