First slide

current density

Question

An electric current flows along an insulated strip PQ of a metallic conductor. The current density in the strip varies as shown in the graph. Which one of the following statements could explain this variation?

Moderate

A

The strip is narrower at P than at Q
B

The strip is narrower at Q than at P
C

The potential gradient along the strip is uniform
D

The resistance per unit length of the strip is constant

Solution

The current density at P is higher than at Q.For the same current flowing through the metallic conductor PQ, the cross-sectional area at P is narrower than at Q.The resistance per unit length r is given by $r = \frac{ρ}{A}$ where $ρ$ is the resistivity and A is the cross-section area of the conductor PQ. Thus, r is inversely proportional to the cross-sectional area A of the conductor.

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