A closely wound, circular coil with radius $2\mathrm{.}40$ cm has $800$ turns.

$($a$)$ What must the current in the coil be if the magnetic field at

the center of the coil is $0\mathrm{.}0580$ T$?($b$)$ At what distance x from the

center of the coil, on the axis of the coil, is the magnetic field half

its value at the center? Ans:$277$A$,0\mathrm{.}0184$m$.$