Drift velocity

From Wikipedia, the free encyclopedia

The drift velocity is the average velocity that a particle, such as an electron, attains due to an electric field. Since particles can accelerate arbitrarily close to the speed of light in the absence of other forces, the term "drift velocity" can only really apply to carriers in materials, and not to particles in a vacuum. Particles in solids, for example, actually collide or scatter with the crystal lattice (or phonons), which slows them down. Drift velocity is non-uniform as it involves electric field as an externally accelerating agent.

In a semiconductor, the two main carrier scattering mechanisms are ionized impurity scattering and lattice scattering.

J_{drift} = \rho \cdot \nu_{avg} where ρ is charge density in units C / cm3, and ʋavg is the average velocity of the carriers

\nu_{avg} = \mu \cdot E where μ is the mobility of the carriers \frac{cm^2}{V-s} and E is the electric field (V/cm)

To find an equation for drift velocity, one can begin with the very definition of current:

I = \frac{\Delta Q}{\Delta t}
where
ΔQ is the small amount of charge that passes through an area in a small unit of time, Δt.

One can relate ΔQ to the motion of charged particles in a wire by:

ΔQ = \left( \mathrm{number \ of \ charges} \right) \times \left( \mathrm{charge \ per \ particle} \right)
= \left( n A \Delta x \right) q
where
n is the number of charge carriers per unit volume
A is the cross sectional area
Δx is a small length along the wire
q is the charge of the charge carriers

Now, normally particles move randomly, but under the influence of an electric field in the wire, the charge carriers gain an average velocity in a specific direction. This is what's called drift velocity, vd. And since Δx = vd Δt, we can plug it into the above equation.

\Delta Q = \left( n A v_d \Delta t \right) q

Putting that back into the original equation and re-arranging to solve for the drift velocity:

v_d = \frac{I}{n q A}


 This condensed matter physics-related article is a stub. You can help Wikipedia by expanding it.
Retrieved from "http://en.wikipedia.org../../../d/r/i/Drift_velocity.html"
Advanced Search
Included Web Search Engines


Safe Search

close

Top Matching Results

Occasionally Search.com will highlight specialized results that are based on the context of your query. Examples of specialized results include specific links to news, images, or video.

Top Matching Results may highlight information from other Search.com pages, content from the CNET Network of sites, or third party content. The listings are based purely on relevance. Search.com does not receive payment for listings in this section but our partners that provide this data may get paid for listing these products.

Sponsored Links

This section contains paid listings which have been purchased by companies that want to have their sites appear for specific search terms and related content. These listings are administered, sorted and maintained by a third party and are not endorsed by Search.com.

Search Results

Search.com sends your search query to several search engines at one time and integrates the results into one list which has been sorted by relevance using Search.com's proprietary algorithm. You can customize the list of search engines included in your metasearch from the preferences.

The search engines that are used in your metasearch may allow companies to pay to have their Web sites included within the results. To view the Paid Inclusion policy for a specific search engine, please visit their Web site. Search.com does not accept payment or share revenue with any search engine partner for listings in this section.