Home » BASIC FUNDA » BIOT- SAVART , MAXWELL LAW

BIOT- SAVART LAW: Baptisle Biot and Felix Savart, in the year 1820 states a law which determines the magnetic field strength surrounding of a current carrying conductor and also calculate the field strength at various point.

Consider a long current carrying conductor carrying current I, and also an infinity small length the current carrying conductor dl. Let a separate point M and the distance between M and dl is x. The direction of current and straight distance(x) between dl and M makes an angle say θ.
Now as per Biot- Savart law,
(i) Magnetic flux density, dB is directly proportional to the current, I. dB∝ I.
(ii) dB at point M is directly proportional to the infinity small length of the conductor dl. So, dB∝ dl
(iii) dB is inversely proportional to the square of the distance of point M and dl. So, dB∝ 1/x2.
(iv) dB is also directly proportional to the sine of the angle makes by the direction of current and straight joining of dl and M. so, dB∝ θ.
Hence, as a equation Biot- Savart law expressed as dB∝ Idlsinθ/x2.
Or, dB=kIdlsinθ/x2. Where k is constant which depends on the magnetic property of the medium.
K=µ0µr/4π.
So, dB= µ0µrIdlsinθ/4πx2.
This law simply relates with ampere’s circuital law. By applying Biot-Savart law we can simply measure the ampere flowing through a conductor like tongue-tester.

MAXWELL CORK SCREW LAW:
By this law we can understand the direction of magnetic field. According to Maxwell, if current flows in a direction from top to bottom of a screw, if we turn the screw with right hand, thumb finger turning movement indicates the direction of magnetic field.

FORCES BETWEEN TWO PARALLEL CONDUCTORS:
If two parallel conductors carrying current in same direction, they attract each other, whereas repeal each other if the current flows through them in opposite direction.
The force between two such parallel conductors is proportional to the product of current strengths and to the length of the conductors considered and varies inversely as the distance between them.
So, F = µ0I1I2L/2πd Newton.
Where I1I2 are the parallel paths current, L= length and d= distance between them.

COMPARISON OF ELECTRIC AND MAGNETIC CIRCUITS:

ELECTRIC CIRCUIT MAGNETIC CIRCUIT
Similarities, Similarities,
1) Exciting force is voltage (E.M.F). 1) Exciting force is Ampere-Turn (M.M.F).
2) Response is current =e.m.f/resistance. 2) Response is Flux (ø)=m.m.f/reluctance.
3) Field intensity is electric field intensity = E/l volt/meter. 3) Magnetic field intensity = NI/l AT/meter.

4) Density is current density =A/m2. 4) Density is Flux density = Wb/m2.
5) Conductance=1/resistance. 5) Permeance=1/reluctance.
6) Conductivity=1/resistivity. 6) Permeability= 1/reluctivity.
dissimilarities, dissimilarities,
1) Resistivity of conductors is constant (temp=constant).

1) Permeability of ferromagnetic material varies greatly with magnetic field strength.

2) Energy must be supplied to maintain the flow of electricity.

2) The magnetic flux once, it is set up, does not require any further supply of energy.

3) Electric current flows. 3) Strictly speaking flux does not flow like electric current.