# Electron drift velocity

1. May 20, 2006

### Brewer

A potential difference of 3.0V is applied to the ends of a copper wire which is 0.5m long. In copper at room temperature, the average time interval between collisions is $$\tau = 2.7*10^{-14}$$s. What is the drift velocity of the free electrons in the wire?

Well, I know that $$V_{d} = \frac{eE\tau}{m}$$, but is E (electric field), just V/d? So it would be 6 (3/0.5)?

If it is that I thought that the electric field was radial due to the wire, and it seems to me that it should be along the wire for the electons to move.

2. May 20, 2006

### big man

V/L is the longitudinal electric field inside the wire and is responsible for exerting a force on a free electron, which is then accelerated along the length of the wire. Then obviously there will be interactions with the atoms in the material, which affect the path/motion of the electrons.

So yeah E = V/L

3. May 20, 2006

### Brewer

Thank you.

4. May 20, 2006

### willydavidjr

So what is the connection of the period(average time interval) between collisions on the problem?

5. May 20, 2006