Question

Eight identical spherical drops, each carrying a charge 1 nC are at a potential of 900 V each. All these drops combine together to form a single large drop. Calculate the potential of this large drop. (Assume no wastage of any kind and take the capacitance of a sphere of radius r as proportional to r).

Answer 1

Let the radius of each drop be r. The capacitance C of each drop is kr, where k is a constant.

Also q = CV, V = 900 volt

:. Charge on each on the eight drops = (kr x 900)C

.'.  Total charge on all the eight drops = Q = 8 q

                                                          =  72A0 kr 

Let R be the radius of the large drop. Then