In a DNA molecule, the base pair adenine and thymine is held together by two hydrogen bonds (see figure below).
Let's model one of these hydrogen bonds as four point charges arranged along a straight line. Using the information in the figure below, calculate the magnitude of the net electric force along this hydrogen bond.
The Attempt at a Solution
Since we are looking at 4 point charges, we need 4 equations. They are:
k = 8.99x10^9 (N*m^2)/C^2
N = -3x10^-10 C
O = -4x10^-10 C
H = 3x10^-10 C
C = 4x10^-10 C
F_no = (k*|N|*|O|) / ((3x10^-10 m)^2) = -1.20x10^10 N -> negative as repelling force
F_nc = (k*|N|*|C|) / ((4.2x10^-10 m)^2) = 6.12x10^9 N
F_ho = (k*|H|*|O|) / ((1.8x10^-10 m)^2) = 3.33x10^10 N
F_hc = (k*|H|*|C|) / ((3x10^-10 m)^2) = -1.2x10^10 N -> negative as repelling force
Since we are asked for find the magnitude of the net electric force, we need to sum all 4 forces together.
ΣF = F_no + F_nc + F_ho + F_hc = 1.54x10^10 N
.... Opps. So I must have done something wrong.
The hint given was "You need 4 eqns: pair N&O, N&C, H&O, H&C and use the charges & distances appropriate for each pair to get a net magnitude between the bases." ... which to my knowledge I have here.
So not sure what I did wrong. Any help would be much appreciated. [/B]