Physics... Coulomb's law
posted by ~christina~ on .
Two small silver spheres with a mass of 10.0g, are separated by 1.00m. Calcuate the fraction of the electrons in one sphere that must be transfered to the other to produce an attractive force of 1.00x10^4 N (about 1 ton) between spheres (number of electrons per atom of silver is 47, and the number of atoms per gram is avogadro's number divided by the molar mass of silver, 107.87g/mol.
I have no idea how to do this.
I know Coulomb's law is Fe= (q1q2)/r^2 but how to find the "fraction" of electrons in one sphere..
help please

You know that q1 must be minus q2 because the electrons that you tranfer from one sphere end up on the other sphere.
You then equate
(q1q2)/r^2 to 1.00x10^4 N
Note that the expression (q1q2)/r^2 for Coulomb force is valid MKS or CGS units not in SI units. The definition of the charge is different in SI units and you then need to include a factor
1/(4 pi epsilon_0).
Once you know the carge q1 you divide it by the charge of an electron. Divide by the total number of electrons to find the fraction.