Two identical copper spheres are separated by 1m in vacuum. How many electrons would have to be removed from one sphere and added to the other so that they now attract each other with a force of  $0.9 N$

Given data: the distance between two identical copper spheres in vacuum is 1m.

Concept solution: work function

Detailed used:

For a force of 0.9N to act between the spheres

 $F=0.9=\frac{1}{4\pi {\epsilon }_0}\frac{q^2}{r^2}$ 

 $q={10}^{-5}C$

The number of electrons added to the sphere by removing it from another can be obtained using the equation :

 n=$\frac{q}{e}$

=$\frac{{10}^{-5}}{1.6\times {10}^{-19}}=6.25\times {10}^{13}\text{ electrons }$