# Two point charges

## Homework Statement

A charge of 0.611 nC is placed at the origin. Another charge of 0.383 nC is placed at x1 = 8.1 cm on the x-axis.
At which point on the x-axis does this potential have a minimum?

U=(kq1q2)/r

## The Attempt at a Solution

I really have no idea how to even start this problem. I've been thinking about it for a couple hours now. Any help would be appreciated.

Last edited:

## Answers and Replies

rl.bhat
Homework Helper
Post the complete question.

I edited the post. My apologies.

And also once I messed up enough the hint was that
"A necessary condition for the potential to have a minimum is that its derivative is 0."

But the derivative of what? The only thing I can think of is the V(r)=kQ/r

rl.bhat
Homework Helper
Potential at a point distance x from q1 is given by

V = k*q1/x + k*q2/(d-x) where d is the distance between the charges.

To find the minimum potential between the charge, find dV/dx and equate it to zero.
And find x.

Thanks a lot! It was kind of a messy derivative but I am so thankful you helped me out. :)