Chapter 21, Problem 21.62P

CP Two identical spheres with mass m are hung from silk threads of length L (Fig. P21.62). The spheres have the same charge, so q₁ = q₂ = q. The radius of each sphere is very small compared to the distance between the spheres, so they may be treated as point charges. Show that if the angle θ is small, the equilibrium separation d between the spheres is d = (q²L/2π∈₀mg)^1/3. (Hint: If θ is small, then tanθ ≅ sinθ.)

Figure P21.62