The energy stored in the magnetic field in a solenoid of length 30cm and diameter 3cm wound with 1000 turns of wire & carrying a current of 10A is
- A. 0.015 joules.
- B. 0.15 joules.
- C. 0.5 joules.
- D. 1.15 joules
Answer: B. 0.15 joules.
Explanation: L = μ0N²A/l = 4π×10⁻⁷×10⁶×(π×0.015²)/0.3 ≈ 2.96 mH; W = ½LI² = ½×2.96×10⁻³×100 ≈ 0.15 J.