Question with large number?electron charge?

  1. Question with large number???electron charge?

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

    The electric charge of an electron is -1.6 x 10^-19 C. What is the force exerted between two electrons separated by one meter? Is it attractive or repulsive?

    2. Relevant equations

    F= K Q1Q2 / D^2

    3. The attempt at a solution

    Im horrible with large numbers and especially at negative exponents....so this is a guess

    K = 9x 10^9 N x m^2/c^2

    Q1 = -1.6 x 10^-19 C
    Q2 = -1.6 x 10^-19 C
    D= 1 m


    F= 9 x 10 ^9 N x m^2 X ( -1.6x 10 ^-19 C x -1.6x 10 ^-19 C / 1^2 m)

    F= 9 x 10 ^9 N x m X (3.2 x 10^19 C^2 )
    F= 28.8 x 10^28 NxmxC^2.....is the answer i got....

    I know i am completely off but how can i do this ...this is basically math but im just not with well large numbers...
     
  2. jcsd
  3. rl.bhat

    rl.bhat 4,435
    Homework Helper

    Re: Question with large number???electron charge?

    F= 9 x 10 ^9 N x m X (3.2 x 10^19 C^2 )
    This step is wrong. -1.6x10^-19 X -1.6x10^-19 = ?
     
  4. Re: Question with large number???electron charge?

    Thats the thing i dont know...do you add the exponents together??

    2.56 x 10^-38????

    1.6 x 1.6 = 2.56 but what about the 10^-19? do i add them or does it stay the same????

    Actually now i got 2.6 x 10 ^-38...by multiplying both
     
    Last edited: Jul 31, 2009
  5. rl.bhat

    rl.bhat 4,435
    Homework Helper

    Re: Question with large number???electron charge?

    This is correct.
     
  6. Redbelly98

    Redbelly98 12,043
    Staff Emeritus
    Science Advisor
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    Re: Question with large number???electron charge?

    Yes, you add the exponents when you are multiplying two numbers.

    Do you have a calculator that you can double-check things like this? If not, Google can be used as a calculator:

    http://www.google.com/#hl=en&q=1.6e...aq=f&oq=1.6e-19+*+1.6e-19&aqi=&fp=MyO-rnw0Pu0

    Note the computer-standard "e-19" to signify "×10-19 "
     
  7. Re: Question with large number???electron charge?

    Ok so after i have 2.6 x 10^-38 is it C^2?
     
  8. Re: Question with large number???electron charge?

    Well let me put what i have..... F=9 x 10^9 N x m^2/c^2 X( 2.6 x 10^-38 c^2 /1 m^2)

    that is what i have...do i cancel out the m^2 and c^2? from both sides? so that only the N is remaining?
     
  9. rl.bhat

    rl.bhat 4,435
    Homework Helper

    Re: Question with large number???electron charge?

    Yes. Force should be in N.
     
  10. Re: Question with large number???electron charge?

    Cool so if i did my calculations right....i got 2.3 x 10^-28 N am i close or am i really off? but i think this force is repulsive no??? because its a positive number .......or is it attractive?
     
  11. rl.bhat

    rl.bhat 4,435
    Homework Helper

    Re: Question with large number???electron charge?

    Like charges repel each other.
     
  12. Redbelly98

    Redbelly98 12,043
    Staff Emeritus
    Science Advisor
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    Re: Question with large number???electron charge?

    Exactly. The equation gives the magnitude of the force. Use the opposites attract / likes repel rule to figure out the direction.
     
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