Looking a electrical potential far away

[seto6]

Homework Statement

V=(KQ/L)((-ln(d))+(ln(L+d)))

is this correct? if not could some one tell me where i went wrong.
thanks in advance.

there is a part 2 to it as follows:

Imagine that distance d is much greater than the length of the rod. Intuitively, the potential should be approximately the same as the potential at a distance d from which of the following charge distributions?

a) an infinitely long wire with total charge Q
b) an infinitely long wire with total charge Qd/L
c) a point charge of magnitude Q
d) an electric dipole with moment QL

V=(KQ/L)((-ln(d))+(ln(L+d)))

not sure what the question trying to interpret, if i am correct as d>>L the charge becomes like a point charge

Homework Equations

V=(KQ/L)((-ln(d))+(ln(L+d)))

The Attempt at a Solution

so my claim is that as we go far we see it as a point charge. but i am not sure about this could someone explain this?

 

[kuruman]

See my posting to part 1

https://www.physicsforums.com/showthread.php?t=408896