# Homework Help: Electric potential and energy

1. Sep 6, 2008

### devanlevin

1000 rain drops, each with a charge of "q" and a potential of "v" fall and make one big drop, losing no charge in the process, what is the potential of the big drop

2. Sep 6, 2008

### alphysicist

Hi devanlevin,

What is the formula for the potential in this case?

3. Sep 7, 2008

### devanlevin

i dont know? KQ/r??? how do i work this out?

4. Sep 7, 2008

### alphysicist

That's right; V=kq/r for each of the small drops. Now relate that to kQ/R for the big drop. What do you get?

5. Sep 7, 2008

### devanlevin

i dont know, how do i know what R is??

6. Sep 7, 2008

### alphysicist

What geometric quantity is the same in the group of 1000 drops as in the one big drop? The radius of the big drop is not 1000 times the radius of a small drop; but what is 1000 times larger in the big drop as in one of the small drops?

7. Sep 7, 2008

### devanlevin

thanks, that should help,,, volume right

8. Sep 7, 2008

### alphysicist

That's right; and with that you can find how much larger the radius of the big drop is compared to the original ones.