Numford

Heat and thermodynamicsClass 11, Thermal Properties of Matter

Dimensional formula of Solar constant

[M T-3]

SI unitwatt per square metre (W/m²)

The solar power reaching one square metre outside the atmosphere, about 1361 W/m². It has the dimension of intensity.

Derivation

How to get the dimensional formula of solar constant

  1. Start from the definition: solar constant = power / area.
  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].
  9. Add the powers of each base quantity: [M T-3].
Same dimensions

Quantities with the dimensions [M T⁻³]

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

Practice

Three questions on solar constant

1Which of these has the same dimensions as solar constant?

2What is the SI unit of solar constant?

3Which one has different dimensions from the others?

Questions

Solar constant: quick answers

What is the dimensional formula of solar constant?

The dimensional formula of solar constant is [M T⁻³]. It comes from solar constant = power / area.

What is the SI unit of solar constant?

The SI unit of solar constant is the watt per square metre (W/m²).

Which quantities have the same dimensions as solar constant?

Solar constant shares [M T⁻³] with heat flux, intensity of a wave, Poynting vector. Equal dimensions do not make them the same quantity.

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