A long plastic rod with rectangular cross section h × w is wound with a coil of length d consisting of N closely packed turns of wire with negligible resistance. A current I runs through the coil....

A long plastic rod with rectangular cross section h × w is wound with a coil of length d consisting of N closely packed turns

of wire with negligible resistance. A current I runs through the coil.

Using the rectangular path of length b shown on the diagram in Figure 22.116, prove that the magnetic field inside the coil

is B = μ0NI/d, and describe the direction of inside the coil.