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

Question 2:

The electrostatic force on a small sphere of charge 0.4 µC due to another small  sphere of charge − 0.8 µC 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?

Solution:

(a) What is the distance between the two spheres?

Given that 

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

Charge on first small sphere,     q₁ =     0.4 µC =   0.4 × 10⁻⁶ C

Charge on second small sphere, q₂ = − 0.8 µC = − 0.8 × 10⁻⁶ C

(1µC = 10 ^{– 6}C    so multiply by 10^{- 6}   there)

The electrostatic force on a small sphere, F = 0.2 N 

Apply Coulomb’s law

q₁ = first charge

q₂ = Second charge

r = distance between both charge

ε₀= permittivity of free space

1/4πε0  = 9 × 10⁹ Nm²C^-2

Plug the values we get 

The distance between the two spheres is 0.12 m.