Numford

Induction, AC and EM wavesClass 12, Alternating Current

Dimensional formula of Power factor

[M0 L0 T0]

SI unitnone, a pure number

The ratio of real power to apparent power, cos φ. It is a pure number between 0 and 1.

Derivation

How to get the dimensional formula of power factor

  1. Start from the definition: power factor = power / power.
  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. displacement = length, so displacement is [L] = [L].
  6. work = force × displacement, so work is [M L T-2] × [L] = [M L2 T-2].
  7. power = work / time, so power is [M L2 T-2] / [T] = [M L2 T-3].
  8. Put in the dimension of each part: [M L2 T-3] / [M L2 T-3].
  9. 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 power factor with the others in the full grid.

Practice

Three questions on power factor

1Which of these has the same dimensions as power factor?

2Which of these has no dimensions at all?

3Which one has different dimensions from the others?

Questions

Power factor: quick answers

What is the dimensional formula of power factor?

The dimensional formula of power factor is [M⁰ L⁰ T⁰]. It comes from power factor = power / power.

What is the SI unit of power factor?

Power factor has no unit, because it is a pure number.

Is power factor dimensionless?

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

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