According to the Biot-Savart law, the magnetic field due to a small current element is inversely proportional to
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → the square of the distance from the element
The Biot-Savart law gives the field \( dB \) of a small current element \( I\,dl \) at a point at a distance \( r \) from it.
\( dB=\frac{\mu_0}{4\pi}\,\frac{I\,dl\,\sin\theta}{r^{2}} \)
Here \( \theta \) is the angle between the element and the line joining it to the point.
Option (1) the current — Incorrect. \( I \) is in the numerator, so the field is directly proportional to the current. Doubling the current doubles the field.
Option (2) the square of the distance from the element — Correct. \( r^{2} \) is in the denominator. So the field falls to one-fourth when the distance is doubled.
NCERT (2026-27):
Magnetic Field Due to a Current Element, Biot-Savart Law – “… According to Biot-Savart’s law, the magnitude of the magnetic field dB is proportional to the current I, the element length |dl|, and inversely proportional to the square of the distance r.”