Wikipedia:Reference desk/Archives/Science/2023 September 27

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September 27

Autumn foliage

Is there any information of dates of beginning, peak and ending in different regions in Europe? And does the foliage come at all to southeastern Europe such as Croatia, Serbia, Romania and Bulgaria? The Finnish Wikipedia says that in southern Finland, the foliage begins in mid-September, peaks in early October and ends in late October and early November. In Central Europe (such as central Germany, southern Poland, Czechia, Slovakia and western Ukraine), the foliage begins in early October, peaks in early November and ends in early December. In northern Italy it begins in mid-November, peaks in early December and ends in early January. Is there any any information about that? --40bus (talk) 14:19, 27 September 2023 (UTC)

Some leads at Deciduous. Click the "59 languages" tab to access information from many countries. 2A02:C7B:113:1E00:8EC:E016:111:57CE (talk) 14:57, 27 September 2023 (UTC)

But it tells nothing about Europe. Where can I find information about that? --40bus (talk) 15:24, 27 September 2023 (UTC)

The Bulgarian, Croatian, Romanian and Serbian words for "deciduous" are respectively широколистни, listopadne, foioase and Листопадни. Typing those words into the search boxes of the relevant Wikipedias (bg, hr, ro, sr) brings up many hits. 2A02:C7B:113:1E00:8EC:E016:111:57CE (talk) 16:23, 27 September 2023 (UTC)

I found Substantial variation in leaf senescence times among 1360 temperate woody plant species

The results suggest that, in contrast to the broader temperature effects that determine leaf out times, leaf senescence times are probably determined by a larger or different suite of local environmental effects, including temperature, soil moisture, frost and wind.

So I'm not sure that you;re going to find a definitive answer.

You may be interested in Climate crisis making autumn leaves fall earlier, study finds.

Alansplodge (talk) 22:01, 27 September 2023 (UTC)

Planck's constant

In wikibook Introduction to Theoretical Physics , chapter 4.5.2 Planck's constant.

You read:

"If you know h (Plank's constant), and you know the frequency of the light, then you can calculate the energy delivered over a certain period of time. For instance, if a beam of light illuminated a target for 3 seconds, and the light frequency was 540 × 10¹² hertz, then the energy delivered would be h × 3 × 540 × 10¹² joules."

So can we replace "3 seconds" by the period associated with the frequency and write "then the energy delivered would be h joules", if not, why not ? Malypaet (talk) 21:40, 27 September 2023 (UTC)

The answer is NO! Your quotation suggests “Introduction to Theiretical Physics” has got it seriously wrong. The frequency of the light multiplied by Planck’s constant gives the energy of one photon of light of the nominated frequency. Dolphin (t) 21:57, 27 September 2023 (UTC)

The quoted sentence implies that h is a dimensionless quantity, while in actuality it has dimension ${\mathsf {M}}{\mathsf {L}}^{2}{\mathsf {T}}^{-1}.$  --Lambiam 07:17, 28 September 2023 (UTC)

Difficult to correct this book on wikibooks which is an offshoot of Wikipedia.

However this sentence raises a question, as a Planck resonator emits a beam of elementary radiation with an energy quanta "E=hv", that this beam can be cut into pulse over a time interval, how many photons emits a resonator in 1 second? Malypaet (talk) 07:20, 28 September 2023 (UTC)

If $P$ is the power output and $\nu$ the wavelength frequency, divide $P$ by $h\nu \,{\text{s}}.$ Note, though, that you cannot just equate quanta with photons. The beam does not consist of individually countable photons – you can only count particles, and these only come into play upon wave function collapse.  --Lambiam 16:47, 28 September 2023 (UTC)

ν is the frequency, not wavelength.

So the number of quanta "nq" in Δt=1s is:

nq=P.Δt/h.ν

And now how can we get the number of resonators emitting this beam with power P ? Malypaet (talk) 21:15, 28 September 2023 (UTC)

Looking at the original Wikibooks entry, that entire section is a disaster from start to finish.

Planck's constant is the constant of proportionality between the energy of a single quanta of electromagnetic radiation and its frequency, as observed by others here. I considered trying to edit the Wikibook, but the more I looked at that page, the more I realized the entire thing needs to be burned to the ground, and I have other stuff to do. PianoDan (talk) 03:29, 29 September 2023 (UTC)

What do you mean by: "a single quanta of electromagnetic radiation" ? An elementary emission from a Planck resonator, or what else? Malypaet (talk) 05:44, 29 September 2023 (UTC)

I mean a photon. "Planck resonators" are not really a modern concept - Planck used them when he was developing his theory, but it's not language anyone uses now. Electromagnetic radiation comes from a variety of sources, but it always consists of photons. PianoDan (talk) 15:03, 29 September 2023 (UTC)

Yes, but the photon is what is emitted. I am more interested in the emitter which is always matter as in thermal radiation. Thermal energy is indeed the agitation of particles in matter and in this case we can very well find the synchrotron effect with its electrons, right? For a radio antenna too, we have electrical energy which is transformed into radiation energy, synchrotron effect too? You replace the virtual Planck resonator object with what in modernity?

Can you list for me the main sources emitting photons? Malypaet (talk) 22:00, 30 September 2023 (UTC)

See Light § Light sources.  --Lambiam 05:47, 1 October 2023 (UTC)