What Is the Potential of the Combined Water Drop?

[Abel I Daniel]

Homework Statement

8 Charged drops of water each of radius 1 mm and having a charge of 10^(-10) Coloumbs are combined to form a bigger drop.Determine the potential of the bigger drop.

Homework Equations

Does the radius becomes 4*10^(-3)m,when it combines?
Does the charge sum up to 9*10^(-10)?

The Attempt at a Solution

[/B]
Used the formula -V=9*10^(9)*Q/r
Got the ans as 1800 V.

 

[Mark44]

Homework Statement

8 Charged drops of water each of radius 1 mm and having a charge of 10^(-10) Coloumbs are combined to form a bigger drop.Determine the potential of the bigger drop.

Homework Equations

Does the radius becomes 4*10^(-3)m,when it combines?

I don't think so. It's probably easier to work with the mm units that were given.
What's the volume of one rain drop?
If you combine 8 rain drops into one bigger drop, what is the volume of this larger drop? What's its radius?

Does the charge sum up to 9*10^(-10)?

The Attempt at a Solution

[/B]
Used the formula -V=9*10^(9)*Q/r
Got the ans as 1800 V.

 

[Abel I Daniel]

I don't think so. It's probably easier to work with the mm units that were given.
What's the volume of one rain drop?
If you combine 8 rain drops into one bigger drop, what is the volume of this larger drop? What's its radius?

I assume the volume to be (4/3)*(pi)*r^3,where r is 1 mm.
But what potential has to do with Volume.i am quit weak in this subject

 

[Mark44]

I assume the volume to be (4/3)*(pi)*r^3,where r is 1 mm.

Or more simply, 4/3 $\pi$, the volume of one rain drop,

But what potential has to do with Volume.i am quit weak in this subject

From the formula you wrote in post #1, the potential V is a function of the radius r.

-V=9*10^(9)*Q/r

If 8 rain drops combine into one larger drop, what's the volume of the larger rain drop? What's the radius of the larger rain drop?

 

[Abel I Daniel]

If 8 rain drops combine into one larger drop, what's the volume of the larger rain drop? What's the radius of the larger rain drop?

i hope it adds up linearliy,that means ,radius of larger frop =8* 1mm (radius of each smaller drop)

 

[Mark44]

i hope it adds up linearliy,that means ,radius of larger frop =8* 1mm (radius of each smaller drop)

No, it doesn't.
The volumes add like you think they would, but the radius of the combined raindrop is NOT 8mm.

 

[Abel I Daniel]

The volumes add like you think they would, but the radius of the combined raindrop is NOT 8mm.

the bigger radius becomes twice the smaller radius ie 2 mm.But what about the charge ?

 

[Mark44]

2 mm is more like it. I'm pretty sure the charge is additive.

 

[Abel I Daniel]

THank you Mark44,for helping me to reach to the answer.You made me think,which i already knew