Calculating Current in a Wire of Given Dimensions

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Homework Help Overview

The problem involves calculating the drift velocity of electrons in a wire given its current, radius, and electron concentration. The subject area pertains to electromagnetism and the behavior of charge carriers in conductive materials.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • The original poster attempts to calculate the drift velocity using the formula involving current, cross-sectional area, electron concentration, and charge. Some participants question the accuracy of the electron concentration value provided, suggesting it may be too low for a metal wire. Others point out a potential error in the cross-sectional area calculation.

Discussion Status

Participants are actively discussing the calculations and assumptions made by the original poster. Some guidance has been offered regarding the electron concentration and the cross-sectional area, but there is no explicit consensus on the final drift velocity value. The original poster seeks clarification on the implications of changing the wire's cross-sectional area.

Contextual Notes

There is a noted discrepancy in the electron concentration value, with participants suggesting typical values for metals. The original poster is also uncertain about the implications of changing the wire's dimensions on the drift velocity.

Johnahh
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Homework Statement


a wire carrying a current of 3.2A has a radius of 1.2mm. the material of the wire has 2.5x10^25 free electrons per cubic metre. the elementary charge is 1.6x10^-19


Homework Equations


I=Anev
cross section = pi*r^2



The Attempt at a Solution


pi*0.0012^2 = 4.5x10^6

3.2/4.5x10^6*2.5x10^25*1.16x10^-19 = 0.1777 recurring
I am sure this is not correct as it seems to fast, I have seen some examples and they are more like 2.8x10^-4 m/s
Am i supposed to make 2.5x10^25 into 2.5x10^19 for mm^3 instead of m^3?
Any help please?
 
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2.5 x10^25 electrons per cubic metre is very low value for a metal wire. It should be in the range 10^28-10^29 electron/m^3.

ehild
 
you have the cross sec area as 4.5x10^6 ...it should be 4.5x10^-6... this is just a typing error and does not affect your answer.
For the figures you have given I also get 0.177
I agree with ehild regarding electron concentration for a metal. 10^28 to 10^29
 
Yeah it was a typo sorry. OK so the electron drift is 0.177 m/s. What happens if the cross section doubles in size is it v*2 or v/2? Thanks
 

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