1. Not finding help here? Sign up for a free 30min tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Charge vs. gravity

  1. Sep 10, 2006 #1

    tony873004

    User Avatar
    Science Advisor
    Gold Member

    Calculate the ratio of the electrostatic force to the gravitational force between two electrons.

    My effort:
    [tex]
    \begin{array}{l}
    \frac{{\left( {\frac{{kq_{electron}^2 }}{{r^2 }}} \right)}}{{\left( {\frac{{GM_{electron}^2 }}{{r^2 }}} \right)}} \Rightarrow \\
    \\
    \frac{{kq_{electron}^2 }}{{GM_{electron}^2 }} = \frac{{8.988 \times 10^9 Nm^2 C^{ - 2} \times \left( { - 1.60217653 \times 10^{ - 19} C} \right)^2 }}{{6.97 \times 10^{ - 11} Nm^2 kg^{ - 2} \times \left( {9.10953826 \times 10^{ - 31} kg} \right)^2 }} = 3.9889 \times 10^{42} \\
    \end{array}
    [/tex]
    Sorry for small tex. This should be better:
    [​IMG]
    My units cancel nicely, so I assume I did it right. However, the book doesn't give the formula I used: F=kqq/r^2

    It gives
    [tex]
    F = Q\left( {E + v \times B} \right)
    [/tex]

    Most text books give you the formulas you need to do the questions at the end of the chapter. So I figure I'd double check here.

    In Wikipedia I looked up the mass and charge of the electron. It gave
    9.109 3826(16) × 10−31 kg
    −1.602 176 53(14) × 10−19 C
    What do the (16) and (14) in these numbers mean?

    *** Edit
    I'm seeing an answer of 10^36 on
    http://en.wikipedia.org/wiki/Fundamental_force
    and 10^39 on
    http://public.lanl.gov/alp/plasma/EM_forces.html
    So I'm a bit less confident about my answer now.
     
    Last edited: Sep 10, 2006
  2. jcsd
  3. Sep 11, 2006 #2

    Andrew Mason

    User Avatar
    Science Advisor
    Homework Helper

    Close but your value for G is too high. G = 6.67x10^11 Nm^2/kg^2. I get 4.17x10^42
    Your approach and method is correct.

    AM
     
  4. Sep 11, 2006 #3

    tony873004

    User Avatar
    Science Advisor
    Gold Member

    Thanks for catching that. I thought I had that memorized.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?



Similar Discussions: Charge vs. gravity
Loading...