Drift Velocity and Current in a Wire – Rankers Physics
Topic: Current Electricity
Subtopic: Relation between Current and Drift Velocity

Drift Velocity and Current in a Wire

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 \(2v\)?
\(2I\)
\(I\)
\(I/2\)
\(I/4\)

Solution:

Since \(I = n e A v_d = n e \pi r^2 v\), the new current is \(I' = n e \pi \left(\frac{r}{2}\right)^2 (2v) = \frac{1}{2} n e \pi r^2 v = I/2\).

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