drift velocity (1 Viewer)

[crynow]

who can tell me the factors that affect drift velocity??

cross area, electron density,tempreture, PD?? or something else??

how do they affect the drift velocity??

tomoro is the day, BEST LUCK for everyone..

 

[kaseita]

I=charge x drift velocity x cross-sectional area x density

charge is constant (electron charge, since we're talking only talking about that)
cross-sectional area constant
density can be affected by temperature
that's it really.

you've basically said it all.
If "I" is constant, then drift velocity is inversely proportional to the rest.
so if density of charge increases, then the electrons will encounter more resistance amongst itself (repelled by other electrons) so drift velocity slows
temperature increase, the lattice has more energy, vibrates more, gets in the way of moving charge
cross-sectional area increases, more lattice structure in the way, and more area for the electrons to go off into different directions, making it harder to get to the other side.

edit: not too sure bout the cross-sectional area one, but that's all I can figure.

 

[superhubert]

remember the formula
I=neva
where
I=current
n=no of electrons
e=charge of electrons
v=drift velocity
a=cross sectional area. you can work it all out from this..
if you decrease the cross sectional area the velocity increases (squeeze your willy next time you take a piddle and see)
its because there is not as much sideways movement by the electrons in there drift velocity (remember drift velocity is a component vector, el;ectrons are still moving everywhich way))

 

[BlackJack]

yep, exactly right.

It's easy to remember too...
"Well I never!" (yes it's a sad pun, but is as good as Oil Rig in Chem...)

 

[kaseita]

I wanted to sink that oil rig...
mainly cause it took me ages to get it into my head
reduction adds
adding reduces

 

[McLake]

What about:

An ox and red cat ....

 

[Wintermute]

No!!!!!!!!

This syllabus point is not entirely correct.

got to:

http://www.phys.unsw.edu.au/~jw/FAQ.html#drift

for an explanation.

The thing is, if you change cross sectional area, you also change the current. So these variables are not proportional, even though the equation I = neva is correct.

The drift velocity is soley dependant on the metal, the field and the charge on the electron. v = constant x E x q

 

[BlackJack]

You mean you want real physics???

I know fully well that this dotpoint is incorrect, and purely doubling cross sectional area will double current (voltage constant). The syllabus assumes that we will falsely think that current was adjusted to be constant.

In the scope of the syllabus deviant behaviour is not needed (and will not be looked kindly upon *thunder, other sounds of threat*. (BoS Dogma number 2165)

edit: hopefully they won't ask screwy question this year, I'll be torn by telling the truth and have tem refuse to discount the question, ot just lie and to hell with scientific accuracy.

 

[McLake]

Real life and physics, have you all gone MAD ...

They can't possibly meet ...

 

[BlackJack]

Oooh... here's one that has been totally disillusioned by high school physics!!!!

The question is Michael, have YOU gone mad? All 'tis studee iz mezn' wit' ya.

 

[spice girl]

Originally posted by BlackJack
to hell with scientific accuracy.

which is why I sometimes like to refer to this subject as "physics", not real physics, just "physics" in quotations...