A small solenoid (radius ra) is inside a largerChapter 28, Problem 28.71
(choose chapter or problem)
A small solenoid (radius ra) is inside a larger solenoid(radius rb > ra). They are coaxial with n a and nb turns perunit length, respectively. The solenoids carry the samecurrent, but in opposite directions. Let r be the radialdistance from the common axis of the solenoids. If themagnetic field inside the inner solenoid (r < ra) is to be inthe opposite direction as the field between the solenoids(ra < r < rb), but have half the magnitude, determine therequired ratio nb/ n a.