512 identical drops of mercury are charged to a potential of 2V each. The drops are joined to form a single drop. The potential of this drop is______ V.

Conserving volume, Vbig =512Vsmall ⇒43πR3=8343πr3⇒R=8rNow, for potential,Vsmall =Kqr    andVbig =Kq'Rhere conserving charge gives ,q'=512q⇒Vbig =K×512q8r=5128Kqr=64Vsmall =64×2⇒Vbig =128 volt