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Magnitude of the electric field in a copper wire.

  1. Oct 22, 2012 #1
    1. The problem statement, all variables and given/known data

    In the circuit shown, two thick copper wires connect a 1.5 V battery to a Nichrome wire. Each copper wire has radius R = 7 mm and is L = 18 cm long. Copper has 8.4 × 10^28 mobile electrons per cubic meter and an electron mobility of 4.4×10^−3 (m/s)/(V/m). The Nichrome wire is l = 5 cm long and has radius r = 3 mm. Nichrome has 9 × 10^28 mobile electrons/m3 and an electron mobility of 7 × 10^−5 (m/s)/(V/m). What is the magnitude of the electric field in the copper wire? Answer in units of N/C
    [​IMG]

    2. Relevant equations

    [itex]\bar{v}[/itex][itex]_{thin}[/itex]=(A[itex]_{thick}[/itex]/A[itex]_{thin}[/itex])[itex]\bar{v}[/itex][itex]_{thick}[/itex]

    [itex]\bar{v}[/itex] = uE

    E=V/L

    3. The attempt at a solution

    I plug in my known values, but I have two unknowns, the electric fields. I'm not sure how to use these equations.
     
  2. jcsd
  3. Oct 22, 2012 #2

    Simon Bridge

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    You also know other stuff: that ##2V_{Cu}+V_{Ni}=1.5V## for example.

    You also know all kinds of physics about the drift velocity, resistance, current etc. to draw on.
    http://en.wikipedia.org/wiki/Drift_velocity
     
  4. Oct 22, 2012 #3
    I had figured it out for a while now but thanks anyway. I just had to use the electron current formula and the voltage loop formula (as you stated); Plug in numbers, solve for e-field and plug in to the other equation.
     
  5. Oct 22, 2012 #4

    Simon Bridge

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    Cool - hopefully someone else stuck on a similar problem will benefit from your question ;)
     
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