The physics
Charge on a metal sphere sits on its outer surface. The sphere's potential is kQ/R, and the field just outside is kQ/R².
V = kQ/R E = kQ/R² = V/R
Joined by a wire: charge flows until both spheres share one potential. So each charge goes as its radius. The smaller sphere gets the stronger field.
Drops that merge: volume and charge both add. The radius grows n1/3 times, the potential n2/3 times.
Earthed: the sphere sits at V = 0. Near a charge q, it takes Q = −qR/d.
C = Q/V = 4πε₀R Vmax = EmaxR
Sparks and glow: air breaks down near 3 × 10⁶ V/m. A big dome reaches millions of volts. A sharp tip glows first, because its radius is tiny.