The magnetic field produced by a current-carrying straight wire at a point outside the wire depends

The magnetic field produced by a current-carrying straight wire at a point outside the wire is governed by the Biot-Savart law and Ampere’s circuital law. For a long straight conductor, the magnitude of the magnetic field (B) at a radial distance (r) is given by the formula B = μ₀I / (2πr). This mathematical relationship demonstrates that the magnetic field strength is directly proportional to the current (I) flowing through the wire and inversely proportional to the distance (r) from the wire. Consequently, as the distance from the wire increases, the magnetic field strength decreases, and the concentric magnetic field lines become more widely spaced. This inverse relationship holds true for all points outside the wire, regardless of whether the distance is short or large.

Sources

1. [1] Science , class X (NCERT 2025 ed.) > Chapter 12: Magnetic Effects of Electric Current > What you have learnt > p. 206