
#1
Nov2112, 04:38 PM

P: 111

Hi all,
I was wondering whether someone might help further understand the following equation for current. I mean get a good picture of how each valuable relates to each other and how they come to represent current. Current = nqvA Thanks. I know what each valuable represents but I can't seem to get a good picture how the equal represents current especially; Where time is taken into account since current is the rate of charge carriers/electrons. I hope I have made my self clear. Thanks. 



#2
Nov2112, 04:45 PM

P: 111

Oops. No need I understand it now.
...but I would appreciate any replies just to make sure. 



#3
Nov2112, 05:12 PM

Sci Advisor
PF Gold
P: 11,353





#4
Nov2112, 05:24 PM

P: 1,351

Current = nqvAq = charge of a charge carrier. (coulomb) v = average speed of charge carriers. (m/s) A = area of crosssection of wire m^2. If you multiply them together you get coulomb/s = Ampere 



#5
Nov2112, 05:36 PM

Sci Advisor
PF Gold
P: 11,353

Just checking we're reading from the same hymn sheet..
This is the 'well known' relationship in which the dimensions are the same each side (that should be reassuring). The way it's derived is to consider a cylinder with of area A and unit length, moving at average speed v. The number of charges in the cylinder will be n times the volume, which is nA (times one, the unit length) so the charge in it will be nqA (per unit length) and the number of charges passing a point in one second will be nqAv. That's I, the current. OK? 



#6
Nov2112, 07:49 PM

P: 315

Googl,
I remember it as: n or p (holes or electrons) = charge carriers q = charge per carrier ±1.6E19 C/(electron or hole) v = velocity A = area So n*q*v*A or p*q*v*A equals current Sometimes J (current density) is used. J = I/A = q*(p or n)*v. EDIT: Sorry, I should have written in the first line, "concentration of n or p (holes or electrons) = charge carriers/m^3 . Ratch 


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