(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

Find the drift velocity in a copper fuse wire with a diameter of 0.22mm. The current is at 5A.

Electronic charge is always 1.6*10^{-19}

Number of de-localised electrons per cubic meter in copper = 1*10^{-19}

2. Relevant equations

I=Avnq

Current = cross-sectional area*drift velocity*number of de-localised electrons*Electroic Charge

3. The attempt at a solution

First i converted the diameter of 0.22mm into radius 0.11mm. Then using pi*r^{2}i have 3.8mm^{2}. Then i converted this into SI to make it 3.8*10^{-3}m^{2}.

So at this point here is the infomation i have.

I=5A

A=3.8*10^{-3}m^{2}

v= ?

n= 1*10^{29}

q=1.6*10^{-19}

I then re-arranged the formula of I=Avnq to make v the subject.

v= __I__

Anq

Then putting in all the numbers i have...

v= ______5______

3.8*10^{-3}m^{2}* 1*10^{29}* 1.6*10^{-19}

Tapping this into my calculator got me the answer of 8.2*10^{-8}ms^{-1}

However this is crazy slow, i know drift velocity is very slow but not this slow. Looking at the answer in the back of the book, for somereason they put it in mm not m, 8.2mms^{-1}. So this in SI should be 8.2*10^{-3}ms^{-1}. This means at some point in my calculations i am 1*10^{5}wrong.

Me and and friends doing this work have been struggling to find out why we are not getting the correct answer. I hope i made sence explaining this to you. We think our errors must be around finding the cross-sectional area, or we had the wrong infomation to begin, such as the number of de-localised atoms in a cubic meter of copper. Or just some mess up of the numbers along the way. Thanks to the people who can help us out here.

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: I = Avnq Where am i going wrong?

**Physics Forums | Science Articles, Homework Help, Discussion**