Summarizing Current

Summary

• Electric current \(I\) is the rate at which charge flows, given by

  \(I=\cfrac{\Delta Q}{\Delta t}\text{,}\)

  where \(\Delta Q\) is the amount of charge passing through an area in time \(\Delta t\).
• The direction of conventional current is taken as the direction in which positive charge moves.
• The SI unit for current is the ampere (A), where \(\text{1 A}=\text{1 C/s.}\)
• Current is the flow of free charges, such as electrons and ions.
• Drift velocity \({v}_{\text{d}}\) is the average speed at which these charges move.
• Current \(I\) is proportional to drift velocity \({v}_{\text{d}}\), as expressed in the relationship \(I={\text{nqAv}}_{\text{d}}\). Here, \(I\) is the current through a wire of cross-sectional area \(A\). The wire’s material has a free-charge density \(n\), and each carrier has charge \(q\) and a drift velocity \({v}_{\text{d}}\).
• Electrical signals travel at speeds about \({\text{10}}^{\text{12}}\) times greater than the drift velocity of free electrons.

Glossary

electric current

the rate at which charge flows, I = ΔQ/Δt

ampere

(amp) the SI unit for current; 1 A = 1 C/s

drift velocity

the average velocity at which free charges flow in response to an electric field