Biot

Pages: 2 (369 words) Published: October 18, 2012
BIOT-SAVART’S LAW OR AMPERE’S LAW FOR CURRENT ELEMENT
Biot-Savart’s law deals with the magnetic field induction at a point due to a small current element. Current element
A current element is a conductor carrying current.It is the product of current,I and length of very small segment of current carrying wire ,dL. Let us consider a small element AB of length dl of the conductor RS carrying a current I. Let r be the position vector of the point P from the current element I dL.and θ be the angle dl and r. According to Biot-Savart’s law,the magnetic field induction dB or magnetic flux density at a point P due to current element depends upon the following factors. (i)                  dB∞I

(ii)                dB∞dl
(iii)               dB∞sinθ
(iv)              dB∞1/r2
Combining these factors,we get
dB∞IdLsinθ/r2
or                                               dB=K Idl sinθ/r2 where K is a constant of perportionality.
In S.I units,                                      K=μ0/4π thus ,                         dB=μ0/4π I dl sinθ/r2 where μ0 is absolute premeability of free space and
μ0=4π*10-7 Wb A-1m-1
= 4π*10-7*TA-1m                                                  [  1T=1 Wb m-2] In C.G.S units,K=1 (In free space)
Thus dB=Idl sinθ/r2
In vector form,
dB=μ0/4π I(dl*r)/r3
magnetic field induction at point P due to current through entire wire is B=∫μ0/4πIdl*r/r3
Or                                    B=∫μ0/4π Idl sin θ/r2 BiotSavart’s law in terms of magnetising force or magnetic intensity (H) of the magnetic field: In S.I System,
dH=dB/μ0=1/4π Idl*r/r3=1/4π Idl*αr/r2
H=∫1/4π Idl*αr/r2
H= ∫1/4π Idl sinθ/r2
Importance OF BIOT SAVART’S LAW:-
1. This law is analogous to Coulomb’s law in electrostatics. 2. Biot Savart’s law is valid for a symmetrical current distribution. 3. This law cannot be easily verified experimentally as the current carrying conductor of very small length cannot be obtained pratically. 4. Biot Sarvart’s law is applicable...