I've learnt that a circular loop of area $A$ carrying a current $i$ produces a magnetic moment equal to $iA$ and the field due to the loop can be considered to be due to a magnetic dipole, consisting of two magnetic charges (magnetic monopoles) - positive (north) and negative (south), each of pole strength $m$ and separated by a distance $d$ such that $md=iA$.
By considering a circular loop carrying a current as a magnetic dipole, the magnetic field could be easily calculated at any point using Coulomb's law of magnetism and law of superposition, instead of using the Biot-Savart law. However, this analogy is not completely perfect because magnetic monopoles have not been observed so far. Also, magnetic field lines do not start or end at a particular point, they only form closed loops and this is contrary to the dipole picture.
Further, the magnetic field inside the dipole system is opposite in direction when compared to that of a circular loop. This can be inferred in the central regions in the following diagrams:
Left: Magnetic field due to a current carrying circular loop.
Right: Magnetic field due to positive (north) and negative (south) magnetic charges (magnetic monopoles) separated by some distance (magnetic dipole).
Image source: Magnetic dipole - Wikipedia
It can be seen that the magnetic field lines are similar in both diagrams except in the central region where the directions are opposite. Also, the field at the assumed pole cannot be determined by using Coulomb's law of magnetism as $r=0$ in $\frac{\mu_0}{4\pi}\frac{m}{r^2}$. However, it can be easily calculated using Biot-Savart law.
My questions are as follows:
Is the magnetic dipole picture of assuming a circular loop carrying a current is a kind of "approximation"? Or in other words, is the field determined by assuming magnetic fields due to magnetic monopoles different from the original field due to circular loop?
In short, how accurate is the magnetic field determined by assuming a circular current carrying loop as a magnetic dipole?Does the pole picture causes variation only in the direction or also includes difference in the magnitude of the field?
Where does the pole picture give accurate result for both magnitude and direction of the magnetic field around a circular loop carrying a current?
What are the specifications for the choice of $m$ and $d$? From $md=iA$, the product $md$ is a constant for a particular $i$ and $A$, however, we're free to choose $m$ and $d$ in such a way it satisfies the condition. So does a small value of $d$ (and large value of $m$) give more accurate results, or is it the other way round?