Homework Help: Electric potential of water droplets

1. Jun 19, 2013

tsgkl

1. The problem statement, all variables and given/known data
Twenty seven charged water droplets each with a diameter of 2 mm and a charge of 10-12 C coalesce to form a single drop .Calculate the potential of the bigger drop.

2. Relevant equations
V(potential)=$\frac{q}{4∏εr}$

3. The attempt at a solution
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Jun 19, 2013

voko

Calculate the potential where? Or do you need to find it as a function?

3. Jun 19, 2013

dreamLord

Well we know that the 27 drops are forming into a bigger drop. So now you have a big drop who's charge and radius is unknown - you have to calculate the potential of that. Try to find out the radius and total charge of the new big drop.

4. Jun 19, 2013

royalhacker

The volume of bigger drop will be equal to volume of 27 small drops
and charge is conserved , so add the total charge

5. Jun 19, 2013

tsgkl

radius came out to be 10-3 m and finally potential came out to be 81V.....thanks for helping guys....

6. Aug 27, 2013

andyrk

How? The radius comes out to be 6x10-3m and not 10-3m. And the potential comes out to be 81/2 Volts and not 81 Volts. Can somebody please verify?

27x4/3x∏x(2)3=4/3x∏x(R)3
=> R3=23.33
=> R=6mm=6x10-3m

=>Vbig drop=1/(4∏εo)xQ/R=9x109x27x10-12/6x10-3=81/2V

??

Last edited: Aug 27, 2013
7. Aug 27, 2013

Staff: Mentor

The problem specifies that the DIAMETER of the small drops is 2mm. The radius of the large drop should turn out to be 3 x 10-3 m , or 3 mm.