4. A very crude model for a neutral water molecule is shown in the figure, a negative "O" and two positive "H's". The geometry has been simplified to make the math easier.
As usual, assume V(infinite)=0.
b) If you bring in a positive test charge (q') from infinite to the origin (the point midway between the two positive hydrogen atoms), at constant speed, keeping the other three charges fixed in position, how much external work do you have to do?
c) After bringing in that test charge (q') to the origin in part b, what is NOW the total stored energy in the system?
Potential at origin,
V_0 = k*(-q)/a + k*(q/2)/a + k*(q/2)/a = 0
Here, k = 1/(4*pi*epsilon_0)
As potential at origin, ...
For a given system of charges, work done to bring another charge from infinity to a specified point is estimated. And then total energy of the system is estimated.