Q4 A very long solenoid having n turns per unit length has radius a. The permeability of the core is . If the magnetic energy density inside of the solenoid is

(un²/2), determine the stored magnetic energy per unit length of the solenoid. (Approx. 5 min.) ooooooo un²12²πa²/4 None of them. u²n² 1²πa²/2 нп2 1 па2 un²²πa³/3 u² n² 1² m² a²/2 μn/ma/2 μ²n² 1²πa²/4 HN2 12 пLa2/2