# Force Between the Strands of DNA Molecule.

1. Homework Statement

The question can be found on this link. It is the last question, the one with the DNA molecules. Prof said that the direction is not important, he is just looking for a magnitude.

http://www.phys.uvic.ca/medphys/people/AJ/Courses/Phys216/Assignments/P216-A1-2007.pdf

2. Homework Equations

Coulomb's law: F=kQq/r^2, where k is 8.987x10^9

3. The Attempt at a Solution

I can get the force between the O and H-N combination of molecules...I think.

F1 = k(0.2e)(0.4e)/(0.280nm - 0.1nm)^2 for the first bond between adenine and thymine.

But I don't know how to get the force between N and H-N.

Are there H's connected to those Nitrogen atom's? If so, would the force just be

F2 = k(0.4e)(0.4e)/(0.300nm - 0.1nm)^2

Thanks!

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Gokul43201
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3. The Attempt at a Solution

I can get the force between the O and H-N combination of molecules...I think.

F1 = k(0.2e)(0.4e)/(0.280nm - 0.1nm)^2 for the first bond between adenine and thymine.
This is only one half of the calculation of the force from the upper bond. You've have correctly calculated the attractive force between O...H, but you also need to calculate the repulsive force between O....N. Remember, you are calculating the net force between the O and the N-H combination (in your own words).

But I don't know how to get the force between N and H-N.

Are there H's connected to those Nitrogen atom's? If so, would the force just be

F2 = k(0.4e)(0.4e)/(0.300nm - 0.1nm)^2
I don't understand your question about H connected to N, but the calculation you need to do here is exactly the same as the one for the previous bond. Again, you've done half the calculation; you need to include the N....N repulsion.