The electrostatic force on a small sphere of charge `0.4muC` due to another small sphere of charge `0.8muC` in air is 0.2 N.
a. What is the distance between the two spheres?
b. What is the force on the second sphere due to the first?

Explanation

`q_(1)=0.4 muC=0.4 xx 10^(-6)C, q_(2)=-0.8 mu C=-0.8 xx 10^(-6)C, F=0.2N`
a. `F=9 xx 10^(6) (q_(1)q_(2))/(r^(2))`
`r^(2)=9 xx 10^(9) xx (q_(1)q_(2))/(F)=(9 xx 10^(9) xx 0.4 xx 10^(-6) xx 0.8 xx 10^(-6))/(0.2) =14.4 xx 10^(-3) =144xx 10^(-4) m^(2) r=12 xx 10^(-2)m`
b. 0.2N, attractive.