The electrostatic force on a metal sphere of charge 0.4 µC due to another identical metal sphere of charge -0.8 µC in air is 0.2N.

Question

(a) The electrostatic force on a metal sphere of charge 0.4 µC due to another identical metal sphere of charge -0.8 µC in air is 0.2N. Find the distance between the two spheres and also the force between the same two spheres when they are brought into contact and then replaced in their initial positions.  

(b) Three small identical balls have charges –3 × 10⁻¹²C, 8 × 10⁻¹²C and 4 × 10⁻¹²C respectively. They are brought in contact and then separated. Calculate (i) charge on each ball (ii) number of electrons in excess or deficit on each ball after contact. 

Answer 1

q₁ = −3 × 10⁻¹²C, q₂ = 8 × 10⁻¹² C, q₃ = 4 × 10⁻¹² C 

(i) The charge on each ball 

(ii) Since the charge is positive, there is a shortage of electrons on each ball. 

∴ Number of electrons = 1.875 × 10⁷