# Elementary Charges

1. Apr 11, 2007

### simplicity12

1. The problem statement, all variables and given/known data
Sphere A with charge -3q is 1.5 m from another identical sphere B with charge +5q. The two spheres are broughtinto contact and then separated by a distance of 1.5 m; the magnitude of the force between the spherees is 8.1 X 10^-2 N.
a. Find the number of electrons transferred from one sphere to the other. Explain which way they moved.

2. Relevant equations
Q=Ne (e=1.602 X 10^-19)

3. The attempt at a solution
I don't really understand the problem. What does it mean when it says that "the two spheres are brought into contact and then separated...". Do i take the average of the charges? The answer for the number of electrons is 1.1 X 10^4. Please help.

2. Apr 11, 2007

### interested_learner

What will happen when the two spheres come together? One has positive charge and one has negative charge. Hmm, do you think that maybe charge will flow? Which direction?

Use Coulomb's law which is:

$$F= \frac {Q_1 Q_2} {4 \pi \epsilon d^2}$$

to get the absolute amount of charge of different sign. Keep in mind that the charge that moves will combine with the positive charge and isn't counted.