(A) The current density $J$ is defined as $J = I/A$,where $I$ is the current and $A$ is the cross-sectional area.Since the current $I$ flowing through

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The strip is narrower at $P$ than at $Q$.

(A) The current density $J$ is defined as $J = I/A$,where $I$ is the current and $A$ is the cross-sectional area.Since the current $I$ flowing through the series conductor $PQ$ is constant,the current density $J$ is inversely proportional to the cross-sectional area $A$ $(J \propto 1/A)$.From the graph,the current density is higher at $P$ and decreases towards $Q$.This implies that the cross-sectional area $A$ must be smaller at $P$ and larger at $Q$.Therefore,the strip is narrower at $P$ than at $Q$.

Class 12 Physics Current Electricity Current Density, Drift Velocity and Mobility

Medium

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?

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 uniform.

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Current Electricity

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Current Density, Drift Velocity and Mobility

The drift velocity of the electrons in a copper wire of length $2\ m$ under the application of a potential difference of $200\ V$ is $0.5\ m/s$. Their mobility (in $m^2 V^{-1} s^{-1}$) is

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The number density of free electrons in a copper conductor is $8.5 \times 10^{28} \; m^{-3}$. How long does an electron take to drift from one end of a wire $3.0 \; m$ long to its other end? The area of cross-section of the wire is $2.0 \times 10^{-6} \; m^2$ and it is carrying a current of $3.0 \; A$.

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$A$ conductor of length $\ell$ with a circular cross-section is shown in the figure,carrying a current $i$. The radius of the cross-section varies linearly from $a$ to $b$. Assuming $(b - a) << \ell$,calculate the current density at a distance $x$ from the left end.

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The drift velocity does not depend upon

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$A$ cylindrical resistor is connected across a battery $\varepsilon$. The cylinder has a uniform free electron density, and the middle part of the cylinder has a larger radius as shown in the figure. Which of the following graphs represents the variation of $V_d$ (drift velocity) with respect to $x$ (distance along the length of the resistor)?

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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?

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The drift velocity of the electrons in a copper wire of length $2\ m$ under the application of a potential difference of $200\ V$ is $0.5\ m/s$. Their mobility (in $m^2 V^{-1} s^{-1}$) is

$A$ conductor of length $\ell$ with a circular cross-section is shown in the figure,carrying a current $i$. The radius of the cross-section varies linearly from $a$ to $b$. Assuming $(b - a) << \ell$,calculate the current density at a distance $x$ from the left end.

The drift velocity does not depend upon

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