Electrical Engineering ⇒ Topic : Biot-Savart Law and its important points.

Biot-Savart law

Biot-Savart law gives us expression for the magnetic field at a point due to a current element.

Important points about  Biot-Savart law. This law has the following salient features :

(1) Biot-Savart law is valid for symmetrical current distributions.

(2)Biot-Savart law cannot be proved experimentally because it is not possible to have a current carrying conductor of length dl.

(3) Like Coulomb's law in electrostatics, Biot-Savart law also obeys inverse square law.

(4) The direction of dB is perpendicular to the plane containing I dl and r

Magnetic Field Intensity (H) due to a Current Carrying Element  - Biot-Savart Law

If an element of length dl of a conductor, measured in the direction of current flow, carries a current of I amperes, then the magnetic field intensity at a point P at a distance r from the element is given by

                                       dH = I d 1 x r l 4 π r³                 ........... (1)

                   FIGURE (a) Magnetic field intensity (H) due to the flow of electric current

where, dH is a vector perpendicular to the plane determined by dl are r as shown in Fig. (a). The value of dH depends on the cross product and therefore changes its sign if the direction of flow is changed.

Equation (1) gives H in A/m when l is in amperes and dl and r are in metres.The value of dH depends upon the position of point P, and is zero when P lies in line with the element. The direction of dH changes as P moves over to the other side of the element as shown in Fig. (b).

                   figure (b) Magnetic field intensity (H) on either side of a current carrying element

Any current carrying conductor must be a closed loop in order to carry the current and the total magnetic field intensity produced by such a loop of wire is given by

                                              ............ (2)