Question

A thin conducting strip of width h = 2.0 cm is tightly wound in the shape of a very long coil with cross-section radius R = 2.5 cm to make a single-layer straight solenoid. A direct current I = 5.0 A flows through the strip. Find the magnetic induction inside and outside the solenoid as a function of the distance r from its axis.

Answer 1

If the strip is tightly wound, it must have a pitch of A. This means that the current will flow obliquely, partly along  and partly along  Obviously, the surface current density is, 

By comparison with the case of a solenoid and a hollow straight conductor, we see that field inside the coil

Note - Surface current density is defined as current flowing normally across a unit length over a surface.