Posted by **Jordan** on Wednesday, February 11, 2009 at 7:19pm.

Two spherical objects are separated by a distance of 2.41 x 10-3 m. The objects are initially electrically neutral and are very small compared to the distance between them. Each object acquires the same negative charge due to the addition of electrons. As a result, each object experiences an electrostatic force that has a magnitude of 4.18 x 10-21 N. How many electrons did it take to produce the charge on one of the objects?

Can you help at all? Please give me an idea where to start. Thank you.

- physics -
**linell**, Wednesday, February 11, 2009 at 7:23pm
F = Q^2 / (4 pi eps d^2)

find Q

then the number electrons is

N = Q /e

where e is the electron's charge (look it up)

- physics -
**drwls**, Wednesday, February 11, 2009 at 7:25pm
The distance between them is

d = 2.41 x 10-3 m

The charge on each sphere is Q

The force of each sphere on the other is

F = k Q^2/d^2 = 4.18 x 10-21 N

Look up the Coulomb's Law constant k and solve that equation for Q.

The number of electrons is

N = Q/e

where e is the electron charge.

- physics -
**Jordan**, Wednesday, February 11, 2009 at 7:53pm
Ok. I did that and I found that Q= 1.64 x 10 ^ -18.

I then divided that by 1.6 x 10 ^ -19.

The answer I got was 10.23.

I am being told that is the wrong answer. Could you please double check that for me?

Thank you!!

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