Two identical conducting spheres with negligible volume have 2.1 nC and –0.1 nC charges, respectively. They are brought into contact and then separated by a distance of 0.5 m. The electrostatic force acting between the spheres is__________× 10–9 N.
[Given : \(4\pi\varepsilon_0=\frac{1}{9\times10^9}\) SI unit]
