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Magnetic field around a wire ? 
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#1
Jan1311, 01:50 AM

P: 2,466

Lets say we have an infinite current carrying wire and it is wrapped with a dielectric materiel.
Lets say the dielectric is 1 cm in diameter around the wire. But lets say I want to find the B field when Im outside the dielectric, Could I just use amperes law . And when im inside the dielectric I would use the H field and then get B by using the magnetic susceptibility of the material . Is this correct . 


#2
Jan1311, 02:22 AM

Sci Advisor
PF Gold
P: 1,765

Off the top of my head I think you can just use the standard magnetic field equation for an infinite wire. The boundary conditions require that the tangential H field be continuous. Since the B field will be described as
[tex]\mathbf{B}(\rho) = \frac{\mu I}{2\pi\rho} \hat{\phi} [/tex] Since the fields are tangential to the inhomogeneity they will not be affected since they will automatically have continous H fields. So this is situation where Ampere's Law will give the correct result. 


#3
Jan1311, 06:05 AM

P: 2,466

Thanks for your response , ok what if i wrapped a superconductor around the wire and cooled it with liquid nitrogen .
And lets say the superconductor goes 1 cm around the wire . Outside the superconductor the B field would be zero , Would amperes law still work? 


#4
Jan1311, 06:33 AM

Sci Advisor
PF Gold
P: 1,765

Magnetic field around a wire ?
Perhaps the best thing to do would be to find the differential equations describing a static magnetic field excited by a static current. Then derive a list of boundary equations dictated by your superconductor and dielectrics and use these in conjunction with your differential equation and solve. This would be similar to, for example, solving the Poisson equation to find the electrostatic field. 


#5
Jan1311, 07:30 AM

P: 2,466

wow , thanks for your answer .



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