A very long solenoid with a circular cross section and radius r= 6.10 cm with n= 1.20E+4 turns/m has a magnetic energy density uB= 4.50 mJ/m3.
a) What is the current in the solenoid?
b) What is the total energy stored in the solenoid if its length is 0.740 meters? (Neglect end effects.)