Electric Current

Summary

Electric current is the rate at which charge flows through a surface.

In equation form, current can be written …

I_ave =	Δq
	Δt

I =	lim		Δq	=	dq
	Δt → 0		Δt		dt

average current

instantaneous current

The SI unit of current is the ampère [A].
- The ampère is a fundamental unit defined by the results of an electromagnetic experiment.
- The unaccented spelling ampere is also acceptable.
- The shortened form amp is often used in informal communication.

Current density is a quantity related to electric current.

The symbol for current density is J (bold).
As a vector it has magnitude and direction.
By definition, current density is the product of charge density (ρ) and velocity (v).
The magnitude of current density is also equivalent to the ratio of current (I) to area (A).

In equation form, current can be written …

J = ρv

J =	I
	A

vector definition

magnitude equivalent

Microscopic Description of Current

The macroscopic phenomena of electric current can be described by the net motion of microscopic charged particles.

In equation form, the microscopic description of current and current density can be written …


I = nqAv	J = nqv
microscopic current	microscopic current density

Where …


I =	electric current [A]
J =	current density [A/m²]
n =	particle density [particles/m³]
q =	charge per particle [C]
v, v =	drift velocity [m/s]
A =	area [m²]