Numford

MagnetismClass 12, Magnetism and Matter

Dimensional formula of Magnetising field

[L-1 A]

SymbolH SI unitampere per metre (A/m)

B divided by μ0 in free space. Its dimension matches magnetisation.

Derivation

How to get the dimensional formula of magnetising field

  1. Start from the definition: magnetising field = magnetic field / permeability of free space.
  2. velocity = length / time, so velocity is [L] / [T] = [L T-1].
  3. acceleration = velocity / time, so acceleration is [L T-1] / [T] = [L T-2].
  4. force = mass × acceleration, so force is [M] × [L T-2] = [M L T-2].
  5. electric charge = electric current × time, so electric charge is [A] × [T] = [T A].
  6. magnetic field = force / (electric charge × velocity), so magnetic field is [M L T-2] / ([T A] × [L T-1]) = [M T-2 A-1].
  7. permeability of free space = force / electric current2, so permeability of free space is [M L T-2] / [A]2 = [M L T-2 A-2].
  8. Put in the dimension of each part: [M T-2 A-1] / [M L T-2 A-2].
  9. Add the powers of each base quantity: [L-1 A].
Same dimensions

Quantities with the dimensions [L⁻¹ A]

Equal dimensions do not make them the same quantity. Compare magnetising field with the others in the full grid.

Practice

Three questions on magnetising field

1Which of these has the same dimensions as magnetising field?

2What is the SI unit of magnetising field?

3Do magnetising field and relative permeability have the same dimensions?

Questions

Magnetising field: quick answers

What is the dimensional formula of magnetising field?

The dimensional formula of magnetising field is [L⁻¹ A]. It comes from magnetising field = magnetic field / permeability of free space.

What is the SI unit of magnetising field?

The SI unit of magnetising field is the ampere per metre (A/m).

Which quantities have the same dimensions as magnetising field?

Magnetising field shares [L⁻¹ A] with magnetisation. Equal dimensions do not make them the same quantity.

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