Biot-Savart law for the magnetic field due to a small current element I dL at point r is:
AdB = (μ₀/4π) I (dL × r̂) / r²
BdB = (μ₀/4π) I (dL · r̂) / r²
CdB = (μ₀/4π) I dL / r
DdB = (μ₀/4π) I dL × r
Answer & Solution
Correct answer: A. dB = (μ₀/4π) I (dL × r̂) / r²
1. dB = (μ₀/4π) · I dL × r̂ / r².
2. r̂ is the unit vector from the source element to the field point.
3. The 1/r² dependence parallels Coulomb's law in electrostatics.
_Source: NCERT Class 12 Physics Ch 4 §4.5 Biot-Savart Law_
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