Question

The energy stored in the magnetic field at a solenoid 100 cm long and 10 cm diameter wound with 1000 turns of wire carrying an electric current of 10 A, is ___________

(a) 1.49 J

(b) 0.49 J

(c) 0.1 J

(d) 1 J

This question was posed to me in unit test.

The origin of the question is Advanced Problems on Millman’s Theorem and Maximum Power Transfer Theorem in chapter Useful Theorems in Circuit Analysis of Network Theory

Answer 1

The correct answer is (b) 0.49 J

The explanation: L = \(\frac{N^2 μ_0  A}{l}\)

= \(\frac{10^6.4π.10^{-7}.\frac{π}{4}.(100 X 10^{-4})}{1}\)

= \(\frac{π^2  X 10^{-3}}{1}\)

Energy = 0.5 LI^2

= 0.49 J.