A very long straight solenoid has a cross-section radius R and n turns per unit length. A direct current I flows through the solenoid. Suppose that x is the distance from the end of the solenoid, measured along its axis. Find:
(a) The magnetic induction B on the axis as a function of x; d caw an approximate plot of B vs the ratio x/R,
(b) The distance x0 to the point on the axis at which the value of B differs by η = 1% from that in the middle section of the solenoid.