To
determine the energy stored in the magnetic field, use the formula: E = ½ LI2
where E is the energy stored, L is the inductance (units: Henry), and I is the
current (units: Ampere).
Correspondingly, L = (µN2A)/l,
where, µ = permeability of medium (in this case, air), N = no. of turns, A = cross-sectional
area, and l = length. Given: N = 68 turns, l = 8 cm, d = 1.2 cm, and I = 0.77
A, other necessary variables are A = 1.13 cm2 and µair =
1.2566 x 10-6 H/m. Applying the formula and checking that the units
agree with each other, the final answer is 2.4352 x 10-6 J.
