Problem 1: Two long thin solenoids are coaxial as shown. The diameter of the inner solenoid is $D_o$, the current is $I_o$, and the winding density (number of
turns per length) is $n_o$. The outer solenoid has four times the diameter, five times the current, and the winding density is one third as large as the inner solenoid. The
length of both solenoids is $200 D_o$.
Part (a) What is the magnetic field vector at the axis of the solenoid?
$B = \mu_o \left(\frac{1}{5}\right) (3I_o)$
Part (b) What is the magnetic field vector at a distance $D_o$ from the axis of the solenoid? This point is outside the inner solenoid since this distance is
twice the radius of the inner solenoid.
Part (c) The inner solenoid has winding density $n_o = 4800$ turns/m, current 1.75 A, and diameter 35 mm. What is the magnitude of the magnetic field at
the central axis? Answer in units of milli-teslas.
$||B|| = $ mT