Ncert Exercises & Solutions

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 remains unaffected. The agent that is essentially responsible for it is:

1.	source of emf
2.	the electric field produced by charges accumulated on the surface of the wire
3.	the charges just behind a given segment of wire which push them just the right way by repulsion
4.	the charges ahead

(b) Hint: The current density depends on the electric field produced.

Current per unit area (taken normal to the current), $\frac{I}{A}$ is called current density and is denoted by $\vec{j}$ . The SI units of the current density are $\frac{A}{m^{2}}$ . The current density is also directed along with E and is also a vector and the relationship is given by is $\vec{j} = σ \vec{E} = \frac{\vec{E}}{ρ}$ . The $\vec{j}$ changes due to the electric field produced by charges accumulated on the surface of the wire.

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