Numford

Heat and thermodynamicsClass 11, Thermal Properties of Matter

Dimensional formula of Latent heat

[L2 T-2]

SymbolL SI unitjoule per kilogram (J/kg)

Heat per unit mass needed for a change of state. It has the same dimension as gravitational potential.

Derivation

How to get the dimensional formula of latent heat

  1. Start from the definition: latent heat = heat / mass.
  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. heat = work, so heat is [M L2 T-2] = [M L2 T-2].
  8. Put in the dimension of each part: [M L2 T-2] / [M].
  9. Add the powers of each base quantity: [L2 T-2].
Same dimensions

Quantities with the dimensions [L² T⁻²]

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

Practice

Three questions on latent heat

1Which of these has the same dimensions as latent heat?

2What is the SI unit of latent heat?

3Do latent heat and internal energy have the same dimensions?

Questions

Latent heat: quick answers

What is the dimensional formula of latent heat?

The dimensional formula of latent heat is [L² T⁻²]. It comes from latent heat = heat / mass.

What is the SI unit of latent heat?

The SI unit of latent heat is the joule per kilogram (J/kg).

Which quantities have the same dimensions as latent heat?

Latent heat shares [L² T⁻²] with gravitational potential. Equal dimensions do not make them the same quantity.

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