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#ferromagnetic material

2 public questions tagged with this topic.

Earth's Magnetism and Magnetic Declination

Which material retains magnetization after the external field is removed and is used in permanent magnets?

**Earth's magnetism** approximated as dipole inclined to rotation axis, magnetic declination is angle between geographic north and magnetic north, inclination or dip angle is angle between total field and horizontal. Horizontal component B_H = B cosδ, vertical B_V = B sinδ, δ dip angle, B_H ≈ 3-4×10⁻⁵ T in India. Ferromagnetic materials, particularly hard ferromagnets, retain magnetization after the external field is removed and are used in permanent magnets. Substituting values gives Ferromagnetic, which matches expected magnitude for this magnetic configuration, confirming dipole field dependence on m/r³ and torque relation τ = m B sinθ.

Ref: NCERT > Physics Book > Magnetism and Matter > Earth's Magnetism and Magnetic Declination

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Torque on Magnetic Dipole and Potential Energy

A ferromagnetic material has \( \mu_r = 1000 \) and \( H = 500 \, \text{A m}^{-1} \). What is the magnetic field \( B \)

**Torque on magnetic dipole** in uniform field B is τ = m × B, magnitude τ = m B sinθ, m moment (A·m²), B field (T), θ angle between m and B (degrees). Torque tends to align moment with field, zero at θ = 0°, maximum mB at 90°, direction given by right-hand rule. B = μ₀ μ_r H . Given: μ_r = 1000 , H = 500 A m⁻¹ , μ₀ = 4π × 10⁻⁷ . Substitute: B = 4π × 10⁻⁷ × 1000 × 500 = 0.628 T ≈ 0.63 T . Substituting values gives 0.63 T, which matches expected magnitude for this

Ref: NCERT > Physics Book > Magnetism and Matter > Torque on Magnetic Dipole and Potential Energy

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