# Homework Help: PD between +q and -q

1. Aug 25, 2011

### Highwaydude

1. The problem statement, all variables and given/known data

Charges +q and -q at points A and B respectively separated by distance R. Required to calculate the potential difference between these 2 points.

2. Relevant equations

I want to do in two ways.. i.e once by integrating the electric field and the other by directly finding the potential at the two points and then subtract them to have the difference

3. The attempt at a solution
Both of my trials have yielded a 2kq/0 which is a bit absurd...
I do like this>
Vb -Va= - ((integration sign)kq/r^2 dr-(int.sign)kq/(R-r)^2 dr)
between the limits 0 to R.. It yields 2kq/0(wth!!)-2kq/R.....
So yeah.. I need help. Oh and K = 1/4pi e0

Last edited: Aug 25, 2011
2. Aug 25, 2011

### physicist2b

please check if you are putting the limit right

3. Aug 25, 2011

### physicist2b

also i dont knw why r u integrating when only two charges are present

4. Aug 25, 2011

### Highwaydude

i am calculating the net electring field... i guess the two kq/0's cancel out one being negative, but its just not coming. i mean bot hare coming out to be positive...

5. Aug 25, 2011

### Highwaydude

Heres the working... sorry, i cant find my mobile phone data cable.. had to do it in paint...

http://hostmypicture.com/images/untitlete.png [Broken]

Last edited by a moderator: May 5, 2017