(B) The drift velocity $v_d$ is given by the formula $v_d = \frac{eE\tau}{m}$,where $E = \frac{V}{l}$.Substituting $E$,we get $v_d = \frac{eV\tau}{ml}

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(B) The drift velocity $v_d$ is given by the formula $v_d = \frac{eE\tau}{m}$,where $E = \frac{V}{l}$.Substituting $E$,we get $v_d = \frac{eV\tau}{ml}$.Since the potential difference $V$ is constant,$v_d \propto \frac{1}{l}$.If the length $l$ is increased to $4l$,the new drift velocity $v_{d'}$ becomes $v_{d'} = \frac{eV\tau}{m(4l)} = \frac{v_d}{4}$.Therefore,the drift velocity decreases by $4$ times.

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

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$A$ constant potential difference is applied between the ends of a wire. If the length of the wire is elongated to $4$ times its original length,then the drift velocity of electrons will be:

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A
increases $4$ times
B
decreases $4$ times
C
increases $2$ times
D
decreases $2$ times

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Current Electricity

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Current Density, Drift Velocity and Mobility

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On increasing the temperature of a conductor,its resistance increases because

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$A$ current $I$ flows through a uniform wire of diameter $d$ when the mean electron drift velocity is $V$. The same current will flow through a wire of diameter $d/2$ made of the same material if the mean drift velocity of the electron is:

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When a potential difference is applied across a linear metallic conductor,then:

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In a wire of cross-section radius $r$,free electrons travel with drift velocity $v$ when a current $I$ flows through the wire. What is the current in another wire of half the radius and of the same material when the drift velocity is $2v$?

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$A$ constant potential difference is applied between the ends of a wire. If the length of the wire is elongated to $4$ times its original length,then the drift velocity of electrons will be:

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