Consider a current carrying wire (current I) in the shape of a ci… - Vidyadip

MCQ

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:

A
Source of emf.
✓
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.

✓

Answer

Correct option: B.

Electric field produced by charges accumulated on the surface of wire.

Key concept: Current per unit area $($taken normal to the current$), \frac{\text{I}}{\text{A}}$, is called current density and is denoted by $\vec{\text{J}}$.

The is unti of the currnt density are $\frac{\text{A}}{\text{m}^2}$. The current density is also directed along $E$ and which is also a vector quantity and the relationship is given by
$\vec{\text{J}}=\sigma\vec{\text{E}}=\frac{\vec{\text{E}}}{\rho}$
where $\sigma$ = conductivity and $\rho =$ resistivity of specific resistance of the the surface of wire.

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