Homework Help: Electricity homework

1. Nov 3, 2008

Jp_Garant

1. The problem statement, all variables and given/known data
Three questions in all. I am unable to find out HOW to get the answer with my text book.
1. An insulator has a positive electric charge of 2.4 x 10^-17 C. How many electrons were added or removed? (^-17 means to the power of negative 17). The answer is 150 electrons removed. However, i am not sure how to get to this answer!

2.If two protons are moved 3 times father apart, the electrical force between them is what factor of the original force? The answer is 1/9. Again, no idea how to get that.

3.If two protons are moved 3 times closer together, the electrical force between them is what factor of the original force? Answer is 9 times greater... how? no idea.

2. Relevant equations
In my text book, i have the following info: which may be used to find the answer, but i dont know how.

Electron------------Mass 9.11 x 10^-31kg-----------Charge -1.60 x 10^-19
Proton-------------Mass 9.673 x 10V-27-------------Charge 1.60 x 10^-19

3. The attempt at a solution

I have tried dividing the charge by 3 and also divding by 3.. as the question suggests factor of 3.. but it obviously doesnt work.. im looking at some equations in the book.. some for current.. I=q/t.. but we have no "t" in these questions.. Pleae help!! I would greatly appreciate, as i have an exam tomorrow!! :)Thanks
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Nov 3, 2008

tiny-tim

Re: Electricity

Hi Jp_Garant!

For 2 and 3, look up Coulomb's law

3. Nov 3, 2008

Jp_Garant

Re: Electricity

Thankyou Tim! I am now able to use this.. tho I needed help... simply because i didnt know how to apply the math. Thankyou :)