Homework Help: physics

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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