64 identical drops each charged upto potential of 10 mV are combined to form a bigger dorp. The potential of the bigger drop will be ____ mV .
Answer: 160
Solution
Combining n identical drops conserves volume, so n⋅34πr3=34πR3, giving R=n1/3r; for n=64 this is R=4r. The total charge becomes Q=nq=64q. A single drop has potential V=rkq=10mV, while the combined drop has V′=RkQ=4rk(64q)=16rkq=16V. The potential of the bigger drop is 160mV.