Biot and Savart conducted many experiments to determine the factors on which the magnetic field due to the current in a conductor depends.

The results of the experiments are summarized as Biot-Savart law.

Let us consider a conductor XY carrying a current I (Fig 3.10). AB = d*l* is a small element of the conductor. P is a point at a distance r from the midpoint O of AB. According to Biot and Savart, the magnetic induction dB at P due to the element of length d*l* is

- directly proportional to the current (I)
- directly proportional to the length of the element (d
*l*) - directly proportional to the sine of the angle between d
*l*and the line joining element d*l*and the point P (sin θ) - inversely proportional to the square of the distance of the point from the element (1/r
^{2})

K is the constant of proportionality

The constant K = μ/4π where μ is the permeability of the medium.

The direction of dB is perpendicular to the plane containing current element Id*l* and r (i.e plane of the paper) and acts inwards. The unit of magnetic induction is tesla (or) weber m^{-2}.

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