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# Physics, AS, electricity question watch

1. A current of 0.4 A flows in a copper wire with a diameter of 0.22 mm. Calculate the mean drift velocity, in m s-1, of the electrons. Using electron number density as 8.0 x 10^28.

I've been trying for a while now and I need it for tomorrow, if you find the answer please state how you did it so I can see where I am going wrong, thanks in advance!
2. So the formula for drift velocity is: I = vAnq
We can rearrange for v: v = I/Anq

Since the wire is basically a circle, we can find the area of it as you are given the diameter.

Plug these into the formula and that should be the answer.
3. Thanks, ive put it all in a few times but i end up getting 8.2237 x 10^-4 however my teacher has got the answer written down as 4.1 x 10^-4 and I really dont understand if he has made a mistake or if ive missed something vital in the calculations
4. Huh, there might be a chance me and my teacher are both incorrect, what did you get for the area?
5. Oh thats where were different, I got 3.8 x 10^-8, howd you get yours?
6. Also, make sure you quote me next time by hitting reply on my message so I get the notification
7. (Original post by hellomynameisr)
Area = pi r^2

0.22mm = 2.2x10^-4m

pi * (2.2x10^-4)^2 = 1.52x10^-7 m^2

Also, make sure you quote me next time by hitting reply on my message so I get the notification
Oh cheers, sorry man, new to the website! Wouldnt it be 1.1 for the radius after halving the diameter
8. (Original post by RobeTG)
Oh cheers, sorry man, new to the website! Wouldnt it be 1.1 for the radius after halving the diameter
Ah yeah...made an amateur mistake (happens when you're sleep deprived )

But yeah, the answer is 8.2x10-4 ms^-1
9. (Original post by hellomynameisr)
Ah yeah...made an amateur mistake (happens when you're sleep deprived )

But yeah, the answer is 8.2x10-4 ms^-1
Its all cool, you have no idea how long it took me to get an answer where I couldnt find any more problems... Never spent so long on a question in my life, anyway thanks a tonne, it helped a bunch having someone with the same answer, enjoy your sleep!

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