Question: Dimensions of permeability are: [PMT/NEET-1991]
a. $A^{2}M^{-1}L T^{-2}$
b. $MLT^{-2}$
c. $M L^{0}T^{-1}$
d. $A^{-4} M L T^{2}$

Answer: a. $A^{2}M^{-1}L T^{-2}$

Solution: From force between two long parallel currents

$F/L=\dfrac{\mu_{0}}{2\pi}\dfrac{I_{1}I_{2}}{r}$.

Thus

$[\mu_{0}] = [F][L][A]^{-2} = (M L T^{-2})\,(L)\,A^{-2} = A^{2}M^{-1}L T^{-2}$

on rearrangement.