A 500turn solenoid is 20 cm long and 19 cm in diameter and c

A 500-turn solenoid is 20 cm long and 1.9 cm in diameter and carries 57 mA . How much magnetic energy does it contain?

Solution

L = mu₀ * N² * A / l = (4 pi * 10^-7 * 500² * pi * (0.95 * 10^-2)²) / (0.20)

L = 0.000445 H

energy stored= 1/2 L I²

= 0.5 * 0.000445 * 0.057²

= 7.23 * 10-7 J = 0.723 muJ