AI Tutor
When you flip a light switch, the bulb lights up almost instantly. But what is physically traveling through that copper wire to make it happen?
The answer is electric current, which measures how much electrical charge passes through a point in a circuit every second.

Defining Electric Current

Quantitatively, electric current (II) is defined as the net rate of charge flow past a specific cross-sectional area over a given time interval.
We express this relationship mathematically as I=Ξ”QΞ”tI = \frac{\Delta Q}{\Delta t}, where Ξ”Q\Delta Q is the charge in coulombs and Ξ”t\Delta t is the time in seconds.
The SI unit of current is the ampere (extA ext{A}), named after French physicist André-Marie Ampère, who established the foundations of electrodynamics in the 1820s.
One ampere equals exactly one coulomb of charge passing a boundary per second: 1Β A=1Β C/s1\text{ A} = 1\text{ C/s}.
Since each electron carries an elementary charge of e=1.602Γ—10βˆ’19Β Ce = 1.602 \times 10^{-19}\text{ C}, how many individual particles are actually moving past that point?

Counting the Electrons

To find the number of charge carriers nn, we divide total charge by the charge of a single carrier: Ξ”Q=nβ‹…e\Delta Q = n \cdot e, which rearranges to n=Ξ”Qen = \frac{\Delta Q}{e}.
Let's work through an example: a small LED flashlight draws a steady current of 0.50Β A0.50\text{ A} for 10Β s10\text{ s}.