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Electrical charges question

  1. Aug 27, 2015 #1
    A molecule of DNA (deoxyribonucleic acid) is 2.09 µm long. The ends of the molecule become singly ionized: negative on one end, positive on the other. The helical molecule acts like a spring and compresses 1.09% upon becoming charged, and remains in this equilibrium position. Determine the effective spring constant of the molecule.

    I did calculate F and I got 5.27*10^-17 then I found x which is 2.27*10^-8
    I found k from the equation k= f/x
    I got 2.31*10^-9 N/m
    But still, it's the wrong answer :(
  2. jcsd
  3. Aug 27, 2015 #2


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    Hello Kdapik. Welcome to PF!

    I get a somewhat larger value for the force F. What did you use for the distance between the charges when you calculated F?
  4. Aug 27, 2015 #3
    2.06*10^-6 m
  5. Aug 27, 2015 #4


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    OK, that's pretty close to what I get (2.07 x 10-6 m). I still don't see how you are getting 5.27 x 10-17 N for the force. Can you show all the numbers that you used to get F?
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