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A current (I) = 12 A and magnetic field (B) = 3 × 10⁻⁵ Wb/m². Consider magnetic field B at distance r. What is the value of r?
- r = μ₀I / 2πB
- r = (4π × 10⁻⁷ × 12) / (2π × 3 × 10⁻⁵)
- r = 8 × 10⁻² m
- None of the above
Correct answer: r = (4π × 10⁻⁷ × 12) / (2π × 3 × 10⁻⁵)
Solution
The magnetic field due to a long straight current-carrying conductor is given by B = μ₀I / 2πr. Rearranging for r, we get r = μ₀I / 2πB. Substituting μ₀ = 4π × 10⁻⁷, I = 12 A, and B = 3 × 10⁻⁵ Wb/m², the correct expression matches option B.
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