Calculating PD between +q and -q Charges at Points A & B

[Highwaydude]

Homework Statement

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

Homework 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

The Attempt at a Solution

Both of my trials have yielded a 2kq/0 which is a bit absurd...
I do like this>
V_b -V_a= - ((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

 

[physicist2b]

please check if you are putting the limit right

 

[physicist2b]

also i don't knw why r u integrating when only two charges are present

 

[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...

 

[Highwaydude]

Heres the working... sorry, i can't find my mobile phone data cable.. had to do it in paint... http://hostmypicture.com/images/untitlete.png