First slide

Drift velocity

Question

Two ends of a metallic wire of uniform cross section are connected to the terminals of a battery. Drift velocity of free electrons is found to be V. If the length of the wire is doubled and cross sectional area is halved, drift velocity of free electrons will be

Moderate

A

4 V
B

$\frac{V}{2}$
C

$\frac{V}{4}$
D

2 V

Solution

$i = n e A v_{d} \frac{V}{R} = n e A v_{d} \frac{V A}{ρ l} = n e A v_{d} \Rightarrow \Rightarrow v_{d} \infty \frac{1}{l} a s l i s i n c r e a s e d b y 2 t i m e s v_{d} d e c r e a s e s b y 2 t i m e s$

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