A coaxial cable (like those used in cable TV installations and withVCRs) consist

Question

A coaxial cable (like those used in cable TV installations and withVCRs) consists of a central conducting wire imbedded in acylindrical insulating core, which is then surrounded by anotherouter conducting cylinder usually made of wrapped aluminum foil orcopper braid. Suppose such a cable carries a currentof 1.80 A flowing in onedirection along the wire and 1.80 A flowing in the opposite directionalong the foil. Use Ampère's Law to find the magnitude ofthe magnetic field at a radialdistance r = 2.0 mm that is between conductors?
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Explanation / Answer

A coaxial cable(like those used in cable TV installations and with VCRs) consistsof a central conducting wire imbedded in a cylindrical insulatingcore, which is then surrounded by another outer conducting cylinderusually made of wrapped aluminum foil or copper braid. Suppose sucha cable carries a current of 1.80 A flowing in one direction along thewire and 1.80 A flowing inthe opposite direction along the foil. Use Ampère's Law tofind the magnitude of the magnetic field at a radialdistance r = 2.0 mm that is between conductors?(T) Only current through the central wire will produce a netmagnetic field between the 2 (inner & outer) conductors. Applying Ampere's Law to the central wire: {Magnetic Field} = B =      = *I/(2*Pi*R)      = (4*Pi*(1.0e-7))*(1.8 A)/(2*Pi*(2.0e-3 m))      = 1.8e-4 T .

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