Answer
$dI=J•dA$
$dA=2rdr$
$dI=(3.00\times10^{8})r^{2}2πrdr$
$dI=(3.00\times10^{8})2πr^{3}dr$
$I=2.5\times10^{-2}A$
Work Step by Step
1. Current is equal to the integral of the dot product of the current density and the area.
2. $dA=2rdr$
3. Integrate the right side of the equation with $.9R$ and $R$ as the limits.
