between a river’s current
and an electric current:
One moves water at a
certain rate, and the other
moves electric charge at a
certain rate.To measure the current, we have to measure how much charge crosses a plane per
unit time. If an amount of charge of magnitude ∆Q crosses an imaginary plane in a
time interval ∆t, then the current is:
Because current is charge per unit time, it’s expressed in coulombs per second. One
coulomb per second is an ampere (abbreviated A), or amp. So 1 C/s = 1 A.
Current vs.
Electron Flow
Remember that current
is in the direction that
positive charges would
move (i.e., opposite the
direction of electron flow).Although the charge carriers that constitute the current within a metal are electrons,
the direction of the current is the direction that positive charge carriers would
move. So, if the conduction electrons drift to the right, we’d say the current points
toward the left.