The magnitude j of the current density in a certain wire with a circular cross section of radius r = 2.11 mm is given by j = (3.25 × 108)r2, with j in amperes per square meter and radial distance r in meters. what is the current through the outer section bounded by r = 0.921r and r = r?

Explanation:

As we know that current density is ratio of current and area of the crossection

now we have

so the current through the wire is given as

now we have

here we have

now plug in the values in above equation

now we have

now plug in both limits as mentioned

here R = 2.11 mm

like poles repel so keep pushing north to north and repels funny to see this