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The energy stored per unit volume in a magnetic field $B = 0.1$ T in vacuum (take $\mu_0 = 4\pi \times 10^{-7}$ N/A²) is approximately:
A$4.0 \times 10^{3}$ J/m³
B$8.0 \times 10^{0}$ J/m³
C$1.59 \times 10^{-3}$ J/m³
D$1.0 \times 10^{-6}$ J/m³
Answer & Solution
Correct answer: A. $4.0 \times 10^{3}$ J/m³
$u_B = B^2/(2\mu_0) = (0.1)^2 / (2 \times 4\pi \times 10^{-7}) = 0.01 / (2.51\times10^{-6}) \approx 3.98 \times 10^3$ J/m³ ≈ 4 kJ/m³.
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