A magnetizing field of \(100 \mathrm{~A} / \mathrm{m}\) produces a magnetic flux of \(2.4 \times 10^{-5} \mathrm{~Wb}\) in an iron bar of cross-sectional area \(0.3 \mathrm{~cm}^2\). The magnetic permeability of the iron bar in the SI unit is

The correct option is (A).
Concept: Magnetic induction \(\mathrm{B}=\frac{\phi}{\mathrm{A}}\),
The permeability is the ratio of magnetic induction and the magnetic field \(\mu=\frac{\mathrm{B}}{\mathrm{H}}\).
Therefore, permeability can be written as \(\mu=\frac{\phi}{\mathrm{AH}}\)
Given values are, \(\mathrm{A}=0.3 \times 10^{-4} \mathrm{~m}^2\) and \(\phi=2.4 \times 10^{-5} \mathrm{~Wb}\)
\(B=\frac{\phi}{A}=\frac{\left(2.4 \times 10^{-4} \mathrm{~Wb}\right)}{\left(0.3 \times 10^{-4} \mathrm{~m}^2\right)}=0.8 \mathrm{~Wb} / \mathrm{m}^2\)
Therefore, \(\mu=\frac{\mathrm{B}}{\mathrm{H}}=\frac{0.8}{1000}=8 \times 10^{-4}\)