Two wires each of radius of cross section $r$ but of different materials are connected together end to end (in series). If the densities of charge carriers in the two wires are in the ratio $1 : 4$, the drift velocity of electrons in the two wires will be in the ratio:
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Let $n_{1}$ and $n_{2}$ be the densities of charge carriers in the two wires, $V_{d_{1}}$ and $V_{d_{2}}$ be the drift velocities of charge carriers in the two wires,

$A$ be the area of cross section,

$e$ is the charge on electron and

$I$ is the current flowing through both the wires

Hence, $I=n_{1} e A V_{d_{1}}=n_{1} e A V_{d_{2}}$

$\therefore n_{1} V_{d_{1}}=n_{2} V_{d_{2}}$

$\therefore \frac{V_{d 1}}{V_{d_{2}}}=\frac{n_{2}}{n_{1}}$

$\therefore \frac{V_{d 1}}{V_{d_{2}}}=\frac{4}{1}$

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