Potential of a point from charged rod.

[Piyu]

Homework Statement

Hello, the problem i have with finding the potential is the integration limits. Assuming both the rod and point lies on the x axis. When i integrate the sum of many slices of rod, ill get 2 answers(negative and positive) depending on the limits i use.

Example i ended up integrating dx/x which means that if i set the far end of the rod as lower limit ill end up with ln(x/L+x) instead of ln((L+x)/X).

So the question is which of it is true and is there a standard way to approach this?

Homework Equations

The Attempt at a Solution

 

[tiny-tim]

Hi Piyu!

Example i ended up integrating dx/x which means that if i set the far end of the rod as lower limit ill end up with ln(x/L+x) instead of ln((L+x)/X).

One is minus the other (logs of inverses) …

and the minus comes because you should have replaced dx by d(-x) if you went the other way!

 

[Piyu]

AH! So whenever i integrate over a variable like dx, it has to go from negative to positive(the right way). Never knew that :P Thanks for the help appreciate it!