A magnetising field of $1600 \mathrm{A}{ \mathrm{m}}^{-1}$ produces a magnetic flux of $2.4\times {10}^{-5} \mathrm{Wb}$ in an iron bar of cross-sectional area $0.2{ \mathrm{cm}}^2.$ The susceptibility of an iron bar is

$H=1600 \mathrm{A}{ \mathrm{m}}^{-1},$

Magnetic flux $\left(\varphi \right)=2.4\times {10}^{-5} \mathrm{Wb}$

$A=0.2{ \mathrm{cm}}^2=0.2\times {10}^{-4}{ \mathrm{m}}^2$

$\therefore B=\frac{\varphi }{A}=\frac{2.4\times {10}^{-5} \mathrm{Wb}}{0.2\times {10}^{-4}{ \mathrm{m}}^2}=1.2{\mathrm{Wbm}}^{-2}$

$\therefore \mu =\frac{B}{H}=\frac{1.2}{1600}=7.5\times {10}^{-4} \mathrm{N}{ \mathrm{A}}^{-2}$

Hence, susceptibility, $\chi =\frac{\mu }{{\mu }_0}-1=\frac{7.5\times {10}^{-4}}{4\pi \times {10}^{-7}}-1=596$