Numford

MagnetismClass 12, Magnetism and Matter

Dimensional formula of Relative permeability

[M0 L0 T0]

Symbolμr SI unitnone, a pure number

The factor by which a material changes B compared with vacuum, so it is a pure number.

Derivation

How to get the dimensional formula of relative permeability

  1. Start from the definition: relative permeability = magnetic field / magnetic field.
  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. Put in the dimension of each part: [M T-2 A-1] / [M T-2 A-1].
  8. Add the powers of each base quantity: [M0 L0 T0].
Same dimensions

Quantities with the dimensions [M⁰ L⁰ T⁰]

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

Practice

Three questions on relative permeability

1Which of these has the same dimensions as relative permeability?

2Which of these has no dimensions at all?

3Which one has different dimensions from the others?

Questions

Relative permeability: quick answers

What is the dimensional formula of relative permeability?

The dimensional formula of relative permeability is [M⁰ L⁰ T⁰]. It comes from relative permeability = magnetic field / magnetic field.

What is the SI unit of relative permeability?

Relative permeability has no unit, because it is a pure number.

Is relative permeability dimensionless?

Yes. Relative permeability is a ratio of like quantities, so every power in its dimensional formula is zero: [M⁰ L⁰ T⁰].

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