Current

Current is defined the amount of Charge moving through a point per second. Conventionally, current is visualised as flowing from a point of high Electrical Potential to a lower Electrical Potential. A lot of things change when charge is moving, as we no longer treat them as static charges.

Definition §

Given a cross sectional area, the current flowing through said area is given by:

Current

$$I=\frac{q}{t}I=\frac{\text{d}q}{\text{d}t}$$

Note

• $I$ = Current (in Amperes, $A=C/s$)
• $q$ = Charge (in $C$)
• $t$ = Time period (in $s$)

Velocities §

There are three different velocities for current, all of them physically meaningful:

• The current signal velocity represent the speed at which electrical effects are passed through a wire. This is close to the speed of light, and explains why telephone communications can be transferred around the globe extremely rapidly.
• The individual electron velocity is the speed of the random electron motion in the wire, and are about one one-hundredth of the speed of light.
• The electron drift velocity is the net velocity at which electrons move in the reference current direction. This is very slow - about a millimetre per second.