#### [SOLVED] Why is charge = nALe

By Jaja

Sorry if this question is a bit broad but I can't find any info on this by just searching.

The equation q = neAL where L is the length of a conductor, A is the area of cross section, n is the number of charges and e is the fundamental charge. This equation clearly does not make sense from a dimensional point of view at first glance. So why is it true and why is it assumed true in most derivations for charge density in terms of drift velocity? #### @garyp 2015-04-30 19:43:02

\$n\$ is the particle density: Number of particles per cubic meter in SI units. \$e\$ would be the charge on a particle (Coulombs), here equal to the elementary charge (they could be protons). With that I think that you will see the the dimensions are correct. #### @Jaja 2015-04-30 19:45:07

Thank you very much. Similar symbols for similar equations can be quite cumbersome to work with. @BySymmetry commented first so I upvoted his comment. I will mark this as the answer when the time limit is up. #### @KidElephant 2015-04-30 20:03:39

A common convention is to use uppercase characters (\$N\$), for extrinsic properties (i.e., the total number), and lowercase characters (\$n\$) for intrinsic properties (number per unit volume). This way, \$q = Ne\$ is also valid, but less informative.