문제)An air-core solenoid with 68 turns is 8.00cm long and has a diameter of 1.20cm. When the solenoid carries a current of 0.770A, how much energy is stored in its magnetic field within the solenoid? 풀이)magnetic field에 stored된 energy를 구하는 공식은 아래와 같다. U = 1/2 × I^2 × LL = μ0 × N^2 × A ÷ l μ0 = 4π × 10^-7 Tm/A N = 68l = 8.00 × 10^-2 mr = 1/2 × 1.20cm = 0.60cm = 6.00 × 10^-3 m A = π × r^2 = 36.0 × 1..