A certain cylindrical wire carries current. We draw a circle of radius r around its central axis in Fig. 26-28a to determine the current i within the circle. Figure 26-28b shows current i as a function of `r^2.` The vertical scale is set by `i_s= 4.0 mA,` and the horizontal scale is set by `r_(s)^(2)= 8.0 mm^(2)`. (a) Is the current density uniform? (b) If so, what is its magnitude? (c) What is the current between r = 0 and r=2.0 mm?

Answer

(a) yes: (b) `199 A//m^(2) approx 2.0 xx 10^(13)A//m^(2)`