# Coulomb's Law & Electrons

1. Mar 2, 2009

### kgigs6

1. The problem statement, all variables and given/known data

Two spherical objects are separated by a distance of 1.98 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 4.19 x 10-21 N. How many electrons did it take to produce the charge on one of the objects?

2. Relevant equations

F = k q1q2/r^2

N= Q/e

k = 8.99E9 nm^2/c^2
e= -1.602E-19C

3. The attempt at a solution

I used coulomb's law and plugged in the Force as 4.19E-21N, boltsmans constant for k and 1.98E-3m as the r^2.

4.19E-21N = (8.99E9Nm^2/C^2)(q^2)/(1.98E-3)^2
1.642E-26N/m^2 = (8.99E9Nm^2/C^2)(q^2)
q = sqrt(1.82719E-36)
q= 1.3517E-18C

N= Q/e
N= (-1.3517E-18C)/(-1.602E-19C)
N= 8.43781 electrons

I've done this over and over and get the same answer but it tells me i'm wrong and i'm not sure what else to try :/
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Mar 2, 2009

### Delphi51

I got the same thing independently. Looks like there is an error in the question.

3. Mar 2, 2009

### kgigs6

Thanks for your help, It's good to know I'm not crazy hah