What is the force between two small charged spheres having charges of 2 × 10⁻⁷ C and 3 × 10 ⁻⁷ C placed 30 cm apart in air?

Since force between two charges q₁ and q2 separated by a distance of r is given by expression:

F=1 /4πε₀   x   q₁q₂/r²

Where ε₀   =Permittivity of free space and value of

1 /4πε₀ =9 X 10⁹ Nm ²C⁻²

and given

Charge on the first sphere, q₁= 2 x 10-⁷ C Charge on the second sphere,

q₂= 3 x 10-⁷ C Distance between the spheres, r = 30 cm = 0.3 m

Therefore

F=9 x 10⁹ x (2 x 10-⁷ x3 x 10-⁷ )/(0.3 )²

F=6 X 10⁻ ³ N

Hence, force between the two small charged spheres is 6 x 10-³ N. The charges are of same nature. Hence, force between them will be repulsive.