First slide

current density

Question

A steady current is flowing through the conductor of variable cross section as shown in the figure. Then select the correct option.

Easy

A

Current through 1 is less than that through 2.
B

Intensity of electric field at 1 is less than that at 2
C

Drift velocity at 1 is more than that 2.
D

Potential difference between sections 1 and 2 is more than the potential difference between the sections A and B

Solution

In a current carrying conductor,
$P = Resistivity = \frac{E}{J} \Rightarrow E = ρ . J = ρ \frac{i}{A}$
Since current i the same at all sections and resistivity is constant $E_{1} < E_{2}$ .
Also, $V_{d} = \frac{j}{n e} = \frac{i}{n e A} \Rightarrow {(v_{d})}_{1} < {(v_{d})}_{2}$
Again, potential drop $= i . R$ . Effective resistance between 1 and 2 is less than that between A and B

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