Problem in Physics

Question

One sphere with a radius of 1cm and another sphere with a radius of 2 cm are distanced with 1m appart, and are tied with the source of the electromotive force ε=3000 V. With what force these spheres interact?

Answer 1

a=1cm, b=2cm,  d=1m,  ε=3000V. The situation describes a capacitor; assume 'plate' a has positive Q and b has -Q.

Approximate the potential at the surface of a to be: V_a=kQ/a,

and at the surface of b: V_b=-kQ/b

Then ΔV= V_a-V_b=kQ/a+kQ/b=kQ[(a+b)/ab]   (ΔV=ε=3000V)  then

Q=(ΔV/k)ab/(a+b)  (calculate Q numerically) and use

Coulumb's law  so that F≈kQ²/d²