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.

Question

I have no idea how to do this.

I know Coulomb's law is Fe= (|q1|q2|)/r^2 but how to find the "fraction" of electrons in one sphere..

help please

Answer 1

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

(|q1|q2|)/r^2 to 1.00x10^4 N

Note that the expression (|q1|q2|)/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.