The mass of an iron rod is 80 g and its magnetic moment is \( 10\,\mathrm{A\,m^{2}} \). If the density of iron is \( 8\,\mathrm{g\,cm^{-3}} \), the magnetisation of the rod is
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → \( 10^{6}\,\mathrm{A\,m^{-1}} \)
The magnetisation of a sample is its net magnetic moment per unit volume, \( M=m_{\mathrm{net}}/V \). The volume of the rod follows from its mass and density.
The volume of the rod is:
\( \begin{aligned} V &= \frac{\text{mass}}{\text{density}} \\ &= \frac{80\,\mathrm{g}}{8\,\mathrm{g\,cm^{-3}}} \\ &= 10\,\mathrm{cm^{3}} \end{aligned} \)
\( V=10\,\mathrm{cm^{3}}=10^{-5}\,\mathrm{m^{3}} \)
The magnetisation is:
\( \begin{aligned} M &= \frac{m_{\mathrm{net}}}{V} \\ &= \frac{10\,\mathrm{A\,m^{2}}}{10^{-5}\,\mathrm{m^{3}}} \\ &= 10^{6}\,\mathrm{A\,m^{-1}} \end{aligned} \)
NCERT (2026-27):
Magnetisation and Magnetic Intensity – “… We define magnetisation M of a sample to be equal to its net magnetic moment per unit volume:
\( \displaystyle \mathbf{M}=\frac{\mathbf{m}_{\mathrm{net}}}{V} \qquad (5.7) \)
M is a vector with dimensions L–1 A and is measured in a units of A m–1.”