One large coil with a thread density of 200 per centimeter is wound on a solid copper rod with a cross-sectional area of 
and next to it is another smaller coil with 15 threads. Calculate the induced voltage in the small coil if a current of 4 A is passed through the large coil and the time required to establish the magnetic field in the large coil is 0.2 s.
The relative permeability 
of copper is 5000 and the permeability of free space is 
.
