The electrostatic force on a small sphere of charge `0.4 muC` due to anther small sphere of charge `-0.8 mu C` in air 0.2 N (i) What is the distance between the two spheres? (ii) What is the force on the second sphere due to the first ?

Explanation

(a)We can use Coulomb.s law
`F=1/(4piepsilon_0)(q_1q_2)/r^2`
`rArr 0.2=9xx10^9xx((0.4xx10^(-6))xx(0.8xx10^(-6)))/(r)^2`
`rArr r^2=9xx10^9xx((0.4xx10^(-6))xx(0.8xx10^(-6)))/0.2`
`=1.44xx10^(-2)`
`rArr r=sqrt(1.44xx10^(-2))` =0.12 m = 12 cm
(b)Both the charged spheres being oppositely charged apply attractive electric force on each other . The force applied by the spheres on each other are equal in magnitude. Therefore , the first sphere attracts the second sphere with a force of 0.2 N.