Normally, we use the letter $f$ to stand for frequency in equations.

$$T = 1/f$$ $$v = \lambda f$$ $$Φ +E_k = h f$$

So I'm curious as why the letter $ν$ (nu) is used to represent frequency in the equation $$E=hν$$ when people who first saw it may think it's velocity due to its resemblance with $v$ and get confused? (And even the frequency formula for matter waves de Broglie deduced from it uses $f$.)

Is there a historical reason behind this?

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    $\begingroup$ Well, actually the first thing is that frequency is almost never denoted with $v$, that letter is actually a Greek letter, $\nu$ (nu), which is a Greek 'n'. I have no idea why people chose to use $\nu$ originally. One possibility is that it stood for 'number', as in the frequency is the number of cycles of the wave per unit time. But that's pure speculation, figuring out how notational conventions started can be a very tricky process that I don't have sufficient energy to pursue. $\endgroup$
    – Andrew
    Commented Oct 15, 2013 at 4:18
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    $\begingroup$ Interesting fact: Both de Broglie in his 1925 thesis (pdf) and Planck in his 1900 paper where he gives his eponymous relation (pdf) use $\nu$ for frequency, despite both French and German using words that begin with "f." Actually, Planck doesn't use the word "Frequenz" at all as far as I can tell, preferring instead "Schwingungszahl" or "Spectralbezirk." $\endgroup$
    – user10851
    Commented Oct 15, 2013 at 7:43
  • $\begingroup$ It seems that this type of soft-questions (v8) ought to be closed since they are in principle abundant (E.g. (i) Why is an electric potential sometimes denoted with a $\phi$? (ii) What is the origin of the naming convention for position functions? etc etc.) and they contain no real physics. $\endgroup$
    – Qmechanic
    Commented Oct 15, 2013 at 11:50

2 Answers 2


I think because scientists in previous centuries had gone through the classical education of ancient greek and latin, and greek, being symbols not used in the normal writing would stand up and not be confused .

Mathematics had used a lot of the first letters ( for every delta there exists an epsilon) and they probably did not want a confusion with force (f). lamda was taken by wavelength ( possibly by association with the l of length). mu, coming before nu in the alphabet, was also used up to denote some constants (magnetic permeability).

This wiki link gives the scientific definitions attached to the greek alphabet, and the correspondence is one letter to many definitions!

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    $\begingroup$ the correspondence is one letter to many definitions which is why we need to start using runes and Tengwar. :D $\endgroup$
    – Kyle Kanos
    Commented Oct 15, 2013 at 14:13

$\nu$ is used more often when specifying electromagnetic waves, such as light, X rays, and gamma rays.

$\omega$ is mostly used by electrical engineers in referring to alternating current.

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    $\begingroup$ That doesn't answer the question $\endgroup$ Commented Oct 15, 2013 at 6:06
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    $\begingroup$ Moreover, 99% of the time in physics $\omega = 2\pi \nu$. The difference is just whether one is dealing with radians or cycles. $\endgroup$
    – user10851
    Commented Oct 15, 2013 at 7:12

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