9. A long, straight solid cylinder, oriented with its axis in the z-direction, carries a current whose current density, J , is given by the following expression: 2 a 2 .70") = 21" [1(:) ]53, when r s a, and j(r)=0, when r 2 a, where a is the cylinder's 5m radius, r is the radial distance from the cylinder's axis, and 1.9 is a constant with units of Ampere. (a) Work out the current passing through the entire cross section of the wire. (b) Using Ampere's Law, derive an expression for the magnitude of the magnetic field, B, in the region r 2 a . (0) Work out an expression for the current passing through a circular cross section of radius r s a and centered at the cylinder's axis. (d) Using Ampere's Law, derive an expression for the magnitude of the magnetic field, B, in the region r s a . How do your results in part (b) and (d) compare for r=a