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Homework Help: Calculate Electric Current

  1. Feb 22, 2014 #1
    1. The problem statement, all variables and given/known data
    Here is the Task:
    The solar wind streams off of the sun in all directions at Speeds of about 400 km/s.
    It contains roughly equal number of electrons and Protons.
    Near the earth we find in a cube with a side length of 1 m about 8.7 * 10^6 Protons. The velocity of These Protons is 470 km/s.

    Find the electric current produced by the flow of These Protons through a cross-sectional area of 1 m^2.

    2. Relevant equations
    The solution should be: 6.6 * 10^(-7)

    3. The attempt at a solution
    I really don't have an idea how to integrate the solar wind into my equation.
    Why is

    (8.7 * 10^6 * 1m^2 * (1.6 * 10^(-19)) / 470 000 m/s


    What has the solar wind to do with that cube?
    Can someone please help me and give me some tips?

    Thanks in advance!
  2. jcsd
  3. Feb 22, 2014 #2
    I don't have a clue on how to treat the solar wind. If "It contains roughly equal number of electrons and Protons" then it should be electrically neuter, so it would not affect the current in any way.

    However I arrived to the solution you mention without considering the wind. Here is how I see it: if we have 8.7 · 10^6 Protons in a 1m² cube then we have [itex]8.7 · 10^6 \frac{protons}{m}[/itex] (note: longitudinal meter here).

    If the protons are moving at 470 Km/s, or 470 000 m/s then we have:

    [itex] 1.6 · 10 ^{-19} \frac{Coulombs}{proton} \times 8.7 · 10^6 \frac{protons}{m}\times 470 000 \frac{m}{s} = 6.5424 · 10^{-7} Coulombs[/itex]

    Which agrees with your solution.
  4. Feb 23, 2014 #3
    Now I understood. Thank you very much for your help.
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