What is the number of excess electrons on each sphere in the following case?Two small spheres spaced 35 cm apart have an equal charge. How many...

The force between two bodies with a charge q1 and q2 and a
distance of separation r is given by Coulomb's law as q1*q2/(4*pi*e0*r^2). 1/(4*pi*e0) =
8.987*10^9 Nm^2/C^2

Now the distance between the spheres in
the problem is 35 cm or 0.35 m.

The force of repulsion is
supposed to be 2.20*10^21 N.

Now the charge on an electron
is −1.602* 10^-19 C

If there are n electrons on
each sphere:

n^2* (-1.602*10^-19)^2*8.987*10^9/0.35 =
2.20*10^21

=> n^2 = 2.2* 10^21*.35 /
(-1.602*10^-19)^2*8.987*10^9

=> n^2 =
3.3*10^48

So n can be taken to be approximately
1.8*10^24.

Therefore each sphere should have
an excess of 1.8*10^24 electrons.