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Question
Consider a current carrying wire (current I) in the shape of a circle. Note that as the current progresses along the wire, the direction of j (current density) changes in an exact manner, while the current I remain unaffected. The agent that is essentially responsible for is ______.
Options
source of emf.
electric field produced by charges accumulated on the surface of wire.
the charges just behind a given segment of wire which push them just the right way by repulsion.
the charges ahead.
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Solution
Consider a current carrying wire (current I) in the shape of a circle. Note that as the current progresses along the wire, the direction of j (current density) changes in an exact manner, while the current I remain unaffected. The agent that is essentially responsible for is electric field produced by charges accumulated on the surface of wire.
Explanation:
Current per unit area (taken normal to the current), I/A, is called current density and is denoted by `vecJ`.
The SI unit of the current density ate A/m2. The current density is also directed along E and which is also a vector quantity and the relationship is given by
`vecJ = σvecE = vecE/ρ`
Where σ = conductivity and ρ = resistivity or specific resistance of the substance.
The `vecJ` changes due to the electric field produced by changes accumulated on the surface of wire.
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