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The magnetic field inside a long straight solenoid with n turns per unit length carrying current I is approximately:
Aμ₀ n I
Bμ₀ I / n
Cμ₀ I / (2 n)
Dμ₀ n²·I
Answer & Solution
Correct answer: A. μ₀ n I
1. Ampère's law applied to a long solenoid gives B = μ₀ n I inside (uniform).
2. Outside the solenoid, B ≈ 0 (far from the ends).
3. Solenoids are common laboratory tools for producing uniform B.
_Source: NCERT Class 12 Physics Ch 4 §4.8 Solenoid_
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