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Assume the chrages to be on the z axis with the midway between them. Find the potential exactly for a field point on the z axis.

Okay, so I found the potential which is v = k*p/(z^2-0.25*l^2)

k is the constant 1/4*pi*epsilon, l stands for the length between the two point charges

The next part of the question asks

How large must z be in order that one can approximate the exact potential on the z axis with the dipole term to an accuracy of 1 percent?

The answer is supposed to be z > 5l, but I don't understand what the question is asking me to do...

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# Multipole Expansion

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