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Posted by on Friday, February 10, 2012 at 9:07am.

An aluminum wire of diameter 2.47 mm carries a current of 12.9 A. How long on average does it take an electron to move 10.5 m along the wire? Assume 3.50 conduction electrons per aluminum atom. The mass density of aluminum is 2.70 g/cm3 and its atomic mass is 27.0 g/mol.

  • Physics - , Friday, February 10, 2012 at 9:19am

    One post of this question is sufficient.

    Ne = (number density of electrons)
    = 3.5 * (number density of aluminum atoms)
    = 3.5 (electrons/atom)* (2.7 g/cm^3)/27 g/mole) *6.02*10^23 atoms/mol
    Ne = 2.1*10*23 electrons/cm^3

    For the velocity of the electrons,
    V = I (Coulombs/s)/[e*(Area)*Ne]

    If wire area in in cm^2, and Ne in electrons/cm^3, this will give you the velocity in cm/s
    e is the electron charge, 1.60*10^19 coulombs/electron

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