Inside a larger coil is a small coil. They are positioned so that their axes are parallel. The current through the large coil is 
and has an opposite direction to the current through the small coil. The large coil is surrounded by 
threads and is 
long. The small coil is wound 
times and is 
long, and a current of 
flows through it. What is the magnetic field density inside the small coil?
.
