Numford

Fundamental constantsClass 11, Thermal Properties of Matter

Dimensional formula of Stefan-Boltzmann constant

[M T-3 K-4]

Symbolσ SI unitwatt per square metre kelvin to the fourth (W/(m² K⁴))

The σ in P = σAT⁴ for a black body.

Derivation

How to get the dimensional formula of Stefan-Boltzmann constant

  1. Start from the definition: Stefan-Boltzmann constant = power / (area × temperature4).
  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] / ([L2] × [K]4).
  9. Add the powers of each base quantity: [M T-3 K-4].
Practice

Three questions on Stefan-Boltzmann constant

1Which is the dimensional formula of Stefan-Boltzmann constant?

2What is the SI unit of Stefan-Boltzmann constant?

3Do Stefan-Boltzmann constant and elementary charge have the same dimensions?

Questions

Stefan-Boltzmann constant: quick answers

What is the dimensional formula of Stefan-Boltzmann constant?

The dimensional formula of Stefan-Boltzmann constant is [M T⁻³ K⁻⁴]. It comes from Stefan-Boltzmann constant = power / (area × temperature⁴).

What is the SI unit of Stefan-Boltzmann constant?

The SI unit of Stefan-Boltzmann constant is the watt per square metre kelvin to the fourth (W/(m² K⁴)).

Is Stefan-Boltzmann constant dimensionless?

No. Stefan-Boltzmann constant has the dimensions [M T⁻³ K⁻⁴].

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