Two positively charged spheres of masses m1 and m2 , are suspended from a common point at the ceiling by identical insulating massless strings of length l. Charges on the two spheres are q1 and q2 , respectively. At equilibrium both strings make the same angle θ with the vertical. Then
m1=m2
tanθ=Fmg (F→same)
tan θ ∝1m
∴m1=m2