**Biot- Savarts' Law:**** **Biot-Savarts' law provides an expression for the magnetic field due to a current segment. The field at a position due to a current segment is experimentally found to be perpendicular to and . The magnitude of the field is

- proportional to the length and to the current and to the sine of the angle between and .
- inversely proportional to the square of the distance of the point P from the current element.

In SI units the constant of proportionality is , where is the permeability of the free space. The value of is

- The expression for field at a point P having a position vector with respect to the current element is

For a conducting wire of arbitrary shape, the field is obtained by vectorially adding the contributions due to such current elements as per superposition principle, where the integration is along the path of the current flow.