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Just wondering about electrons.

  1. Mar 18, 2007 #1
    3. In a lightning bolt, it is estimated that a charge of -20 C is transferred from a cloud to the Earth. How many electrons make up such a lightning bolt?

    N = Q/e

    N = -20c / 1.6 x 10^-19

    N = -1.25x10^20

    I'm pretty sure this is the right answer. What I'm wondering is... how can I have a negative number of electrons? This makes this formula seem flawed to me. I guess I can just remove the negative sign after the fact, is that what most people do?
  2. jcsd
  3. Mar 18, 2007 #2
    If you are going to take e to be a positive number, then the charge of the electron has to be -e. You have a positive number of particles. Good that you recognized that your answer didn't make sense.
  4. Mar 18, 2007 #3
    The electrical charge is either positive or negative. The Coulomb was defined as positive (since it is the amount of charge carried by 1A for one second and the current is defined as going from positive voltage to negative). So a quantity of electrons is negative since they have negative change.
  5. Mar 18, 2007 #4
    This is the formula we were given:

    Q = Ne

    Where Q is the charge in coulombs, N is the number of electrons,
    and e is the elementary charge (1.6 x 10^-19 C).

    So the elementary charge is actually -1.6 x 10^-19 C whenever you're dealing with electrons?
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