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The magnetic field (dB) due to a small element (dl) at a distance (r) and element carrying current i is
- dB = μ₀/4π (i dl × r)/r
- dB = μ₀/4π (i dl × r)/r²
- dB = μ₀/4π (i dl × r)/r³
- dB = μ₀/4π² (i dl × r)/r
Correct answer: dB = μ₀/4π (i dl × r)/r³
Solution
The Biot-Savart law states that the magnetic field dB due to a current element is proportional to the current (i), the length of the element (dl), and the sine of the angle between dl and the position vector r, and inversely proportional to the cube of the distance r. Hence, the correct formula is dB = μ₀/4π (i dl × r)/r³.
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