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Homework Help: Hydrogen discharge question

  1. Sep 25, 2006 #1
    I have been trying to figure out what the equation is for this problem:

    A glass tube filled with gas has electrodes at each end. When a sufficiently high potential difference is applied between the two electrodes the gas ionizes; electrons move towards the positive electrod, and the positive ions move toward the negative electrode. a) What is the current in a hydrogen discharge if, in each second, 3.6 * 10 ^18 electrons and 1.15 * 10 ^18 protons move in the oppisite directions through a cross section of the tube?

    I am not sure what the equation(s) is to solve this problem. I have searched my book to see if I can find something similar to this but have not been able to find anything that discusses this topic.
  2. jcsd
  3. Sep 25, 2006 #2


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    Staff Emeritus
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    Current is the charge (moving) per unit time.

    The current in this case is composed of negative charges (electrons) and positive charges (protons), which move more slowly since they are heavier.

    By convention, the current is in the direction of the movement of positive charge, which means in the direction of proton movement, and opposite the direction of the electron movement.

    I = (np*qp - ne*qe)/ 1 sec.

    The - sign before the electron contribution indicates that the electrons are moving opposite the protons. The charge on the qe[/sup] = -qp.

    np = number of protons, ne = number of electrons

    and q = magnitude of charge of the proton (+) and electron (-)
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