Physics · Magnetism And Matter · NEET
No. Magnetic moment (m) is a property of the whole object and its unit is A·m². Magnetisation (M) is the magnetic moment packed into each unit of volume, so M = m_net / V and its unit is A/m. Two bars can have the same M but different total moment if their volumes differ.
Ampere per metre (A/m). Check it by dimensions: magnetic moment is A·m², volume is m³, so A·m² / m³ = A/m. Interestingly this is the same unit as magnetic intensity H, which is why NEET questions often relate M and H directly through M = χH.
H (magnetic intensity) is the field you apply from outside (from the coil/solenoid current). M (magnetisation) is the material's own response — how much it has itself become magnetised. For a linear material they are linked by M = χH, where χ is susceptibility.
It is a vector. M points in the direction of the net aligned dipole moments. For paramagnetic and ferromagnetic materials M points along H; for diamagnetic materials M points opposite to H, which is why their susceptibility χ is negative.
The total field inside a material is B = μ₀(H + M). Here μ₀H is the applied part and μ₀M is the extra field the magnetised material adds. Rearranging gives M = B/μ₀ − H, a form used in many numericals.
Try the real previous-year questions from this chapter — each with the answer and a full solution.
M = net magnetic moment / volume = m_net / V. For a linear material it also equals M = χH, where χ is the magnetic susceptibility and H is the magnetic intensity.
Ampere per metre (A/m), the same unit as magnetic intensity H.
B = μ₀(H + M). This means M = B/μ₀ − H. It shows the total field B is the applied part μ₀H plus the material's contribution μ₀M.
For a linear (para/dia) material, magnetisation is proportional to the applied intensity H. The constant χ (susceptibility) is positive for paramagnetic, small; negative for diamagnetic; and very large for ferromagnetic materials.
M links a material's own response to the applied field and connects directly to susceptibility χ and permeability μ. Numericals on iron rods and solenoid cores use M = χH and B = μ₀(H+M).
