First slide

Magnetic properites of materials.

Question

The number of atoms per unit volume in a sample of iron is 9 × 10²⁸atoms /m³. The magnetic moment of every iron atom is 1.5×10^–23 Am². If all dipoles are aligned in a domain due to ferromagnetic interaction, then magnetic moment and the pole strength of the rod of length 10 cm and area of cross - section 1cm² is

Difficult

Solution

$\begin{array}{rcl} M & = & 9 x 10^{28} x 1.5 x 10^{- 23} x 10^{- 5} = 13.5 A - m^{2} \\ m & = & \frac{M}{2 l} = \frac{13.5}{10^{- 2} x 10} = 135 A - m \end{array}$

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