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410 views
09:55 Nov-06-2000
John Kitzmiller
magnetic fields!

Does D.C. currrent pick up surface discontinuities as well as
A.C. current? If not then what is the differential?


 
02:11 Nov-06-2000
dave ronson
Re: magnetic fields! : Does D.C. currrent pick up surface discontinuities as well as
: A.C. current? If not then what is the differential?

Sure it does. However, AC will find surface indications must easier since it
>is a less penetrating current. Whereas DC has the ability to penetrate the
>material much easier due to the current being Direct and not alternating as
>in AC. The alternating aspect of AC allows the particles to "dance" on the
>surface allowing the particles to attract to a discontinuity much easier.





 
07:15 Nov-07-2000

Michael Trinidad

Consultant, API 510 570 & 653
Marine Inspection Service Pty Ltd (MIS),
Australia,
Joined Jan 2003
138
Re: magnetic fields! : : Does D.C. currrent pick up surface discontinuities as well as
: : A.C. current? If not then what is the differential?

AC current passing through a conductor reverses its direction of flow at a regular frequency so that the electron movement is restricted to the surface of the conductor. The higher the frequency at which the current alternates then the greater will be the “skin effect”. As a consequence the magnetic field associated with AC flow is confined at or near the surface of the material.

DC current flows in a constant direction through a conducting material so that the electrons are moving throughout its cross section and length, although the movement is practically negligible at its centre becoming more pronounced as the surface is neared. The effect of passing DC through a conductive material is that the density of the resulting magnetic field is greatest at the surface of the conductor and becomes progressively weaker in a linear manner, as it penetrates towards the centre.

Kindest Regards


Michael Trinidad



 


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