- Electric current is the rate at which charge flows through a surface.
- Electric current is often just called current.
- As a scalar, current has magnitude only.
- The symbol for current is I (italic).
- In equation form, current can be written as…
non-calculus version calculus version Iave = Δq Δt I = lim Δq = dq Δt → 0 Δt dt average current instantaneous current
I = electric current [A] ∆q, dq = charge passing through some area [C] ∆t, dt = interval, instant of time [s]
- 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 in written English.
- The shortened form amp is often acceptable or even prefered.
- The SI unit of charge is the coulomb [C]
- The coulomb is a derived unit.
- One coulomb is the amount of charge transferred by one ampère of current in one second of time [C = A s].
- Current density is a quantity related to electric current.
- The symbol for current density is J (bold).
- As a vector, current density 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 density can be written as…
J = ρv J = I A vector definition magnitude equivalent J, J = current density [A/m2] as a vector or its scalar magnitude I = electric current [A] ρ = charge density [C/m3] v = drift velocity [m/s] A = area [m2]
- The SI unit of current density is the ampère per square meter [A/m2].
- 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 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]