Current
Electric current is the flow (movement) of electric charge. The SI unit of electric current is the Ampere (A), which is equal to a flow of one Coulomb of charge per second. Electric current is measured using an ammeter. more...
Home
Action Figures
Beanies
Accessories
Bammers/ Bamm Beanos
Disney/ Pooh Beanies
Other Beanies
Ty Attic
Ty Beanie Babies
Current
Bears
Birds
Bunnies
Cats
Collections/ Bulk Lots
Dogs
Farm Animals
Monkeys
Mythical Creatures
Other Current Beanie Babies
Sea Creatures
Seasonal
Wild Animals
Retired
Bears
Birds
Bunnies
Cats
Collections/ Bulk Lots
Dogs
Farm Animals
Monkeys
Mythical Creatures
Other Retired Beanie Babies
Sea Creatures
Seasonal
Wild Animals
Ty Beanie Boppers
Ty Beanie Buddies
Ty Beanie Kids
Ty Pillow Pals
Ty Plush
Ty Teenie Beanies
Ty Trading Cards
Construction Toys & Kits
Diecast & Vehicles
Toys & Games
Wargames & Role-Playing
Definition
The amount of electric current (measured in amperes) through some surface, e.g., a section through a copper conductor, is defined as the amount of electric charge (measured in coulombs) flowing through that surface over time. If Q is the amount of charge that passed through the surface in the time t, then the average current I is:
By making the measurement time T shrink to zero, we get the instantaneous current i(t) as:
The ampere, the measure of electric current, is an SI base unit so that the coulomb, the measure of electric charge, is derived from the definition of the ampere.
Current in a metal wire
In solid conductive metal, a large population of electrons are mobile or free electrons. These electrons are bound to the metal lattice but not to any individual atom. Even without an external electric field applied, these electrons move about randomly due to thermal energy but on average, there is zero net current within the metal. Given an imaginary plane through which the wire passes, the number of electrons moving from one side to the other in any period of time is exactly equal to the number passing in the opposite direction.
When a metal wire is connected across the two terminals of a DC voltage source such as a battery, the source places an electric field across the conductor. The moment contact is made, the free electrons of the conductor are forced to drift toward the positive terminal under the influence of this field. The free electron is therefore the current carrier in a typical solid conductor. For an electric current of 1 ampere rate, 1 coulomb of electric charge (which consists of about 6.242 × 1018 electrons) drifts every second through the imaginary plane through which the conductor passes.
The current I in amperes can be calculated with the following equation:
where
It follows that:
Current density
-
Current density is a measure of the density of electrical current. It is defined as a vector whose magnitude is the electric current per cross-sectional area. In SI units, the current density is measured in amperes per square meter.
Read more at Wikipedia.org
|