College Physics 10th Edition by Raymond Serway,Chris Vuille

Exercise 41

A certain superconducting magnet in the form of a solenoid of length 0.50 m can generate a magnetic field of 9.0 T in its core when its coils carry a current of 75 A. The windings, made of a niobium titanium alloy, must be cooled to 4.2 K. Find the number of turns in the solenoid.