# Homework Help: Electric Fields

1. Nov 24, 2005

### dekoi

1.) If 1.00g of hydrogen is seperated into electrons and protons, and the protos are placed on Earth's north pole while the electrons on the south pole, what is the resulting compressional force on Earth?
So i would need to get the attractive force of the electrons and protons at the north and south poles. I could use the formula
$$F_e = k_e \frac{q_e q_p}{r^2}$$
Where q_e is the charge of the electrons and q_p that of the protons. The r (i suppose) would be half of the circumference of earth. Correct? The biggest problem is getting the number of electrons and protons from the mass of the hydrogen. How do i do this?! Im sure im overlooking somethign.
2.) This is a general theory question.
Suppose i have 2 stationary charges x-distance apart. Another charge is on the same axis and is movable. What does it mean for the system of charges to be in stable equilibrium? I would assume it means for the net force on charge three to be 0.
If i am told to solve for the position of charge three in respect to the other two stationary charges, i equate the two forces acting on it and solve for "x". But i could get two values for x (its a second-degree equation). I always thought that it makes more sense to take the positive value, since that would mean the third charge lies in between the other two, but the answer sheet tells me otherwise. One of the answers says that the distance of the third charge is (e.g.) -1.54cm. How would stable equilibrium be reached if the charge is not even in the middle of the other two?

2. Nov 24, 2005

### Astronuc

Staff Emeritus
In #1, r is the separation between the charges. So with protons at one pole and the electrons at the other, one must use the polar diameter for r. This is a classic physics problem.

1 gram of H = 1 gram-mole of H = Avogadro's number of H atoms which gives the same number of protons and electrons.

3. Nov 24, 2005

### dekoi

Yes, that worked. Thank you.