PHYS 230 Lecture Notes - Lecture 6: Interactive Voice Response, Density, Terminal Velocity
Document Summary
Suppose a collection of charges is moving perpendicular to a surface of area a, as shown in the figure. Current magnitude is determined by the potential difference v and the resistance r. The electric current i is defined to be the rate at which charges flow across the area a. If an amount of charge q passes through a surface in a time interval t, then the current i is given by q=i t; I= q/ t (i"s unit is 1 coulombs per second =1a, 1 ampere). The current density (j"s unit is 1 ampere per square meter = 1a/m2) is a concept closely related to current and describes the current direction and intensity per unit cross-section area. The magnitude of the current density j at any point in space is the amount of charge per unit time per unit area flowing pass that point. That is, j = q/( t a) it is also true. j = i/ a.
