# Excess electrons or protons on drop.

## Homework Statement

A small drop of water is suspended motionless in air by a uniform electric field that is directed upward and has a magnitude of 8450 N/C. The mass of the water drop is 3.80 10-9 kg.

(b) How many excess electrons or protons reside on the drop?

## The Attempt at a Solution

i'm not sure what i'm doing wrong, but i get about 4.1071 x 10^-12 C

and for the drops i get 2.754 x 10-31

not sure why its wrong?

i used this for formula, see image: http://img180.imageshack.us/img180/6734/80350082pv3.png [Broken]

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Kurdt
Staff Emeritus
Gold Member
I'm not sure what you're asking here really. I presume the image is the answer to the question and you're wondering why yours is different. From the 2.754x10-31 it appears you've multiplied the charge on the drop by that on a proton.

well the image has different values to be calculated, and the image was just another example to show what was going on,

the problem i calculated was different, but it should still be calculated the same.

and it should be: 2.75e+07 but not sure why???

hage567
Homework Helper
i'm not sure what i'm doing wrong, but i get about 4.1071 x 10^-12 C

and for the drops i get 2.754 x 10-31

not sure why its wrong
I'm getting slightly different numbers than you, but are you sure you're dividing by the electron charge and not multiplying? That's the only way I can see you getting an answer with that magnitude.