What is Current and the coulomb?

Also known as: electric current · ampere · coulomb

Definition 12.1 High School Physics · Chapter 12 — Electric Circuits and Power

An electric current is an ordered flow of charge (electrons, in a metal). Its intensity $I$ , in amperes ( $\mathrm{A}$ ), is the charge passing through a cross-section of the wire per second: a steady current $I$ flowing for a time $t$ transports the charge

q = I\,t ,

in coulombs ( $\mathrm{C}$ ), with $1\,\mathrm{C} = 1\,\mathrm{A}\,\mathrm{s}$ . The elementary charge is $e = 1.6 \times 10^{-19}\,\mathrm{C}$ . Current is measured by an ammeter, inserted in series.

Examples

Example 12.2 (Lightning versus phone)

A lightning stroke carries some $3.0 \times 10^{4}\,\mathrm{A}$ for about $1.0 \times 10^{-4}\,\mathrm{s}$ : $q = 3.0\times10^{4} \times 10^{-4} = 3.0\,\mathrm{C}$ . Your phone, at $2.0\,\mathrm{A}$ , moves the same charge every $1.5$ seconds.

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