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| The '''drift velocity''' is the average [[velocity]] that a particle, such as an [[electron]], attains due to an [[electric field]]. It can also be referred to as axial drift velocity since particles defined are assumed to be moving along a plane. In general, an electron will ‘rattle around’ in a [[Electrical conductor|conductor]] at the [[Fermi velocity]] randomly. An applied electric field will give this random motion a small net velocity in one direction.
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| In a [[semiconductor]], the two main carrier scattering mechanisms are [[ionized impurity scattering]] and [[lattice scattering]].
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| Because current is proportional to drift velocity, which is, in turn, proportional to the magnitude of an external electric field, [[Ohm's law]] can be explained in terms of drift velocity.
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| Drift velocity is expressed in the following equations:
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| <math>J = \rho v_{\it avg}</math> | |
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| <math>v_{\it avg} = \mu E</math>
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| where <math>J</math> is the [[current density]], <math>\rho</math> is [[charge density]] (in units [[Coulomb|C]]/m<sup>3</sup>), and <math>v_{\it avg}</math> is the drift velocity, and where <math>\mu</math> is the [[electron mobility]] (in units (m^2)/[[volt|V]]*s) and <math>E</math> is the [[electric field]] (in units V/m).
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| ==Mathematical formula==
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| The formula for evaluating the drift velocity of charge carriers in a material of constant [[cross-section (geometry)|cross-section]]al area is given by:<ref>{{cite book|last=Griffiths|first=David|title=Introduction to Electrodynamics|year=1999|publisher=Prentice-Hall|location=Upper Saddle River, NJ|page=289|edition=3}}</ref>
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| <math>v={I \over nAq}</math> | |
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| where {{math|''v''}} is the drift velocity of electrons, {{math|''I''}} is the current flowing through the material, {{math|''n''}} is the charge-carrier density, {{math|''A''}} is the [[area]] of [[cross section (geometry)|cross-section]] of the material and {{math|''q''}} is the [[electric charge|charge]] on the charge-carrier.
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| In terms of the basic properties of the right-[[cylindrical]] [[electrical current|current]]-carrying [[metal]]lic [[electrical conductor|conductor]], where the charge-carriers are [[electrons]], this expression can be rewritten as {{Citation needed|date=June 2013}}:
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| <math>v={MV \over d N_A \ell e f \rho_0 (1+\alpha_0 T)}</math>
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| where,
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| *{{math|''v''}} is again the drift velocity of the electrons, in {{math|''[[metre|m]]·[[second|s]]''}}<sup>−1</sup>;
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| *{{math|''M''}} is the [[molar mass]] of the metal, in {{math|''[[kg]]·[[mole (unit)|mol]]''}}<sup>−1</sup>;
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| *{{math|''V''}} is the [[voltage]] applied across the conductor, in [[volt|{{math|''V''}}]];
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| *{{math|''N''<sub>A</sub>}} is [[Avogadro’s number]], in {{math|''[[mole (unit)|mol]]''}}<sup>−1</sup>;
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| *{{math|''d''}} is the [[density]] ([[mass]] per unit [[volume]]) of the conductor, in {{math|''[[kg]]·[[metre|m]]''}}<sup>−3</sup>;
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| *{{math|''e''}} is the [[Elementary charge|fundamental electric charge]], in [[coulomb (unit)|{{math|''C''}}]];
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| *{{math|''ρ''<sub>0</sub>}} is the [[resistivity]] of the conductor at 0{{math|''°C}}, in ''{{math|[[ohm (unit)|''Ω]]·[[metre|''m'']]}}'';
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| *{{math|''α''<sub>0</sub>}} is the [[temperature coefficient#Temperature coefficient of electrical resistance|temperature coefficent of resistivity]] of the conductor at 0{{math|''°C''}}, in [[kelvin (unit)|{{math|''K''}}]]<sup>−1</sup>;
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| *{{math|''T''}} is the [[temperature]] of the conductor, in {{math|''[[degree Celcius|°C]]''}},
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| *{{math|''{{unicode|ℓ}}''}} is the [[length]] of the conductor, in {{math|''[[metre|m]]''}}; and
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| *{{math|''f''}} is the number of [[free electrons]] released by each [[atom]].
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| == Numerical example ==
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| Electricity is most commonly conducted in a copper wire. [[Copper]] has a density of 8.94 g/cm³, and an [[atomic weight]] of 63.546 g/mol, so there are 140685.5 mol/m³. In 1 [[Mole (unit)|mole]] of any element there are 6.02×10<sup>23</sup> atoms ([[Avogadro's constant]]). Therefore in 1m³ of copper there are about 8.5×10<sup>28</sup> atoms (6.02×10<sup>23</sup> × 140685.5 mol/m³). Copper has one free electron per atom, so ''n'' is equal to 8.5×10<sup>28</sup> electrons per m³.
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| Assume a current ''I'' = 3 amperes, and a wire of 1 mm diameter (radius in meters = 0.0005m). This wire has a cross sectional area of 7.85×10<sup>−7</sup> m<sup>2</sup> (''A'' = π×0.0005<sup>2</sup>). The charge of 1 [[electron]] is ''q''=−1.6×10<sup>−19</sup> Coulombs. The drift velocity therefore can be calculated:
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| <math>v={I \over nAq}</math>
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| <math>v= {3 \over \big({{8.5 \times 10^{28}} \big) \times \big({7.85\times 10^{-7}} \big) \times \big({-1.6 \times 10^{-19}} \big)}}</math>
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| <math>v={-0.00028} \text { m/s}\,\!</math>
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| Analysed dimensionally:
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| [v] = [amperes] / ( [electron/m<sup>3</sup>] × [m<sup>2</sup>] × [coulombs/electron] )
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| := [coulombs] / ( [seconds] × [electron/m<sup>3</sup>] × [m<sup>2</sup>] × [coulombs/electron] )
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| := [coulombs] / ( [seconds] × [meters<sup>-1</sup>] × [coulombs] )
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| := [meters] / [second]
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| Therefore in this wire the electrons are flowing at the rate of −0.00029 m/s, or very nearly −1.0 m/hour.
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| By comparison, the Fermi velocity of these electrons (which, at room temperature, can be thought of as their approximate velocity in the absence of electric current) is around 1570 km/s.<ref>http://230nsc1.phy-astr.gsu.edu/hbase/electric/ohmmic.html Ohm's Law, Microscopic View, retrieved Feb 14, 2009</ref>
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| In the case of [[alternating current]], the direction of electron drift switches with the frequency of the current. In the example above, if the current were to alternate with the frequency of F = 60 Hz, drift velocity would likewise vary in a sine-wave pattern, and electrons would fluctuate about their initial positions with the amplitude of:
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| <math>A = (1/2F) (2\sqrt{2}/\pi)|v| = 2.1\times10^{-6} \text{m}</math>
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| ==See also==
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| *[[Electron mobility]]
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| *[[Speed of electricity]]
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| *[[Drift chamber]]
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| *[[Guiding center]]
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| ==References==
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| <references/>
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| <!-- Other Project Links -->
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| ==External links==
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| * [http://hyperphysics.phy-astr.gsu.edu/hbase/electric/ohmmic.html Ohm's Law: Microscopic View] at Hyperphysics
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| {{DEFAULTSORT:Drift Velocity}}
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| [[Category:Condensed matter physics]]
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Conventional wisdom is the fact that it happens to be fairly difficult to get rid of weight, however, that's not true in the event you understand how to go regarding doing this. It is important to learn all which is required to get rid of weight to aid yourself achieve the objective more easily. Continue reading this particular article to discover about the greatest way to approach losing weight.
We are certain that you'll have each success in finding diets that work whenever hunting over these proven systems. Great luck with the weight loss plans.
It refuses to matter how little the weight loss is. When it comes to diet plans, should you find one which gives we a outcome then you've got a winner. stay with it!
Since the health of the bones is an significant piece of how you function, milk treatments ought to be a piece of the diet. Cheeses and lotions will be significant inside fat, so you should be careful whenever buying for those particularly. Labels that say +low fat+ only indicate they're lower in fat than general + they could nevertheless be chock full of the stuff. Try skim milk rather. It's a wonderful source of calcium without the high amounts of fat and calories.
There are a number of favored diets that simply do not work alone. Therefore, it is very significant to join a gym to have a backup program. Although a decrease in total calories will assist you lose fat or slow the weight gain, exercise may aid we burn calories plus increase a weight loss. The ultimate objective should be to change your lifestyle so that we consume less calories than you burn.
A objective is a great deal of points, it's as much as we. If you want to minimize the salt intake, shed 10 lbs or stop eating a whole lot of processed foods we can do it. Begin a diary involving your goals, and take entries about how you're advancing.
I eat a variety of food when I'm dieting to avoid aspects from getting boring. There are tons of healthy recipes available plus I might try to add any healthy recipes when I can think of them. In the mean time here are my favorite healthy dishes which I like to eat at least a couple of times a week.