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Homework Help: Electrons in GRAMS

  1. Sep 3, 2009 #1
    Electrons in GRAMS :(

    1. The problem statement, all variables and given/known data


    A sample of electrons is found to have a total charge of -7.68 x 10^8 C.
    How many electrons are in this sample ?
    Part 2 says:

    What is the mass of the above sample of electrons in grams ?

    2. Relevant equations
    1 electron mass = 9.10938188 × 10^-28 grams]

    3. The attempt at a solution

    for part 1 My answer was 4.79e27. And its CORRECT

    for part 2 i keep getting 4.36 as an answer but its wrong.

    I used [1 electron mass = 9.10938188 × 10^-28 grams]

    and multiplied that by my answer for part 1.

    PLEASE HELP, Thanks.
  2. jcsd
  3. Sep 3, 2009 #2


    User Avatar
    Homework Helper

    Re: Electrons in GRAMS :(

    How about keeping a couple more digits in that 4.79e27?
  4. Sep 3, 2009 #3
    Re: Electrons in GRAMS :(

    tried that and got 4.366556698 and was still wrong even using only 3 sig figs

    Help please
  5. Sep 3, 2009 #4
    Re: Electrons in GRAMS :(

    How are you checking your answer?
  6. Sep 3, 2009 #5
    Re: Electrons in GRAMS :(

    its a quiz online, tells me whether im correct or incorrect

    Any more help guys ?
  7. Sep 4, 2009 #6
    Re: Electrons in GRAMS :(

    Hmm, multiple choice or one of those annoying computer quizzes that counts an answer wrong when it's misspelled, has a space left out, etc?

    The math looks OK to me, it could just be the quiz expects something like spelling out units rather than using the abbreviation.
  8. Sep 4, 2009 #7
    Re: Electrons in GRAMS :(

    no its fill in the blank, but it specifically says "IN GRAMS" and "WITHOUT UNITS" and since the first part I got right with only 3 sig figs, I thought that was my problem here, but it was still wrong.

    Help please.
  9. Sep 4, 2009 #8
    Re: Electrons in GRAMS :(

    Sorry I got the same answer as you, must be something wrong with the quiz

    Stay Up
  10. Sep 4, 2009 #9


    User Avatar

    Staff: Mentor

    Re: Electrons in GRAMS :(

    I understand you have tried 4.37?
  11. Sep 5, 2009 #10
    Re: Electrons in GRAMS :(

    ya I got the problem fixed it wasn't my answer that was wrong it was a technical error.

    Thanks for the help guys !!
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