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

A. source of emf.
B. electric field produced by charges accumulated on the surface of wire.
C. the charges just behind a given segment of wire which push them just the right way by repulsion.
D. the charges ahead.

Explanation

electric field produced by charges accumulated on the surface of wire.
Current flowing per unit cross section normal to
Flow is called current density j = `(I)/(A)` . Its SI unit is `Am^(-2)` . It is vector quantity and its direction is in direction of electric field. vector relation is given by j = `sigma`E.
When charge is accumulated on surface of the wire electric field is produced and current density changes.