Differences

This shows you the differences between two versions of the page.

--- 184_notes:extra_words [2018/01/26 19:23] – created dmcpadden
+++ 184_notes:extra_words [2018/01/27 18:43] (current) – dmcpadden
@@ Line 1: / Line 1: @@
+==== Conventional Current vs Electron Current ====
+===Electron Current ===
+Before, we defined the electron current as the number of electrons passing through a point per second. Because the electron current is made up of negative charges, the electron current will always flow opposite to the electric field. (This is a more general rule that you may remember from before - electrons will always move opposite to the direction of the electric field.) We will use a lower-case "i" to represent the electron current.
+ $i=\frac{\# electrons}{second}$
+We can generally write the electron current in terms of the **electron density** in the wire ( $n$ ), which gives the number of electrons per volume of the wire that are free to move, the cross-sectional area of the wire ( $A$ ), and the average speed of the electrons through the wire.
+ $i=nAv_{avg}$
+If we check the units of this equation we see that:
+ $\frac{\# electrons}{s}=\frac{\# electrons}{m^3}*m^2*\frac{m}{s}$
+===Conventional Current ===
+Conventional current is then defined as the number of coulombs passing through a point per second. In this case, we can find this by multiplying the electron current by the magnitude of the charge of an electron. If the charge carriers aren't electrons (e.g., some kind of ion), then you will need to use the charge of the charge carrier. We will use an upper-case "I" to represent the conventional current.
+ $I=\frac{\# Coulombs}{second}=|q|i$
+The conventional current is now positive (number of electrons times the magnitude of the charge). By "convention", the conventional current flows in the opposite direction of the electron current. In other words, the conventional current will flow in the //same// direction as the electric field. The units of conventional current are  $\frac{Coulombs}{second}=\frac{C}{s}=A$ , which we call an Ampere or an Amp for short.
+For historical reasons, much of what we work with in circuits is based off of conventional current rather than the electron current (much of what we know was established before we discovered it was the electrons that were free to move; you can thank [[https://en.wikipedia.org/wiki/Benjamin_Franklin#Electricity|Ben Franklin]] for that). However, remember that physically, the electrons are what move in a circuit.
 ===== Motivating Moving Charges =====