Numford

OpticsClass 12, Wave Optics

Dimensional formula of Fringe width

[L]

Symbolβ SI unitmetre (m)

The spacing of bright fringes in Young's experiment, λD/d.

Derivation

How to get the dimensional formula of fringe width

  1. Start from the definition: fringe width = wavelength × length / length.
  2. wavelength = length, so wavelength is [L] = [L].
  3. Put in the dimension of each part: [L] × [L] / [L].
  4. Add the powers of each base quantity: [L].
Same dimensions

Quantities with the dimensions [L]

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

Practice

Three questions on fringe width

1Which of these has the same dimensions as fringe width?

2What is the SI unit of fringe width?

3Which one has different dimensions from the others?

Questions

Fringe width: quick answers

What is the dimensional formula of fringe width?

The dimensional formula of fringe width is [L]. It comes from fringe width = wavelength × length / length.

What is the SI unit of fringe width?

The SI unit of fringe width is the metre (m).

Which quantities have the same dimensions as fringe width?

Fringe width shares [L] with length, displacement, radius of gyration, mean free path, wavelength, amplitude, focal length, de Broglie wavelength. Equal dimensions do not make them the same quantity.

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