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33 votes
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When a candle burns, why does the top of wick glow if bottom of flame is hottest?

The wick temperature does not have to be the same as the flame temperature.The flame is hottest at the bottom, but the wick is hottest at the top. For a candle, the wick burning isn't the intended ...
A.K.'s user avatar
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29 votes

When a candle burns, why does the top of wick glow if bottom of flame is hottest?

Because fire is not the same thing as light. Michael Faraday did a wonderful job of explaining how the candle works, and I direct you to look at it (there are also Youtube videos giving a modern take ...
Zhe's user avatar
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22 votes
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How were x-ray diffraction patterns deciphered before computers?

I agree with @andselisk that this question is quite broad. I will focus on two specific questions asked The only equation I know for x-ray diffraction is Bragg's Law but is this the only equation ...
Karsten's user avatar
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19 votes
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Does all fire only emit light on its outermost shell?

The answer is NO. The article you quote makes a completely unwarranted generalisation that "all flames are hollow". This is true of some flames but only because the fuel that is burning is ...
matt_black's user avatar
16 votes
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How would you know if the light emitted is of one wavelength or if it is a mixture of two or more wavelengths?

The green light from copper flame is sadly not a single wavelength. It is very good question though because not many students even think about it. In order to "see" what wavelengths are ...
ACR's user avatar
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14 votes
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Why does the same electron transition release photons of different frequencies for some elements?

I am glad that you updated the question because it highlights a very common misconception. First of all the JavaLab Flame Test is completely wrong for both copper, calcium and many more salts ...
ACR's user avatar
  • 41.2k
13 votes

How does molecular structure contribute in the property of fluorescence?

Keep in mind a few things that must happen for an absorption process to result in fluorescence: (1) the initial transition is to an excited electronic state that observes certain rules regarding the ...
Buck Thorn's user avatar
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10 votes

Why does calcium emit circularly polarized light?

Photons have a spin of magnitude $1$. If we project the corresponding spin state vectors onto the momentum vector of the photon, we get what's called "helicity" with values $\pm1$ which are ...
Antimon's user avatar
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8 votes
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Cause of continuous spectral lines

The spectral lines represent transitions between pairs of discrete energy levels in the atom; an electron is excited by absorbing the energy of a photon and a transition from one of these levels to ...
porphyrin's user avatar
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8 votes

Why objects usually don't exibit fluorescence/phosphorescence?

You are correct in most of what you write. Absorption in the visible (and uv) parts of the spectrum are of far larger energy that IR and microwave and the lowest electronic transition involves ...
porphyrin's user avatar
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7 votes
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Ultraviolet Movie

In thin layer chromatography (TLC), plates coated with silica, or alumina often include such an inorganic fluorescent manganese doped zinc silicate dye which is activated by black light/UV light of $\...
Buttonwood's user avatar
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6 votes

What is the role of a monochromator in atomic absorption spectrometer?

The answer by @bobthechemist is clear, concise and correct and I upvoted it. However, I think the first figure in bobthechemist’s answer does not fully convey the significant complexity of the ...
Ed V's user avatar
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6 votes

What is the role of a monochromator in atomic absorption spectrometer?

This question has lingered on the site for a long time, which is a shame because it is a good question to ask. Atomic absorption spectroscopy (AAS) uses a hollow cathode lamp (HCL) as a source, and ...
bobthechemist's user avatar
5 votes

How to Combine an Emission spectrum into a colour?

It is not simple -- for example, to many people, red + blue spectral lines appear purple/violet, i.e., shorter wavelength than pure blue! Though you could assign a color name to a pure spectral line, ...
DrMoishe Pippik's user avatar
5 votes

How were x-ray diffraction patterns deciphered before computers?

Not just in the '20s but up to the '90s at least, the d-spacings were estimated by hand measurements of diffractometer peaks or film lines and applying the Bragg formula. d-spacings were then ranked ...
Trunk's user avatar
  • 239
4 votes
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What molecules are produced in carbon arc lamp and how do they produce light?

Answers: Consider the mass and kinetic energy of an electron or of an ion of nitrogen or oxygen, and the reactivity with carbon. Good question! It would be interesting to see the relative abundance ...
DrMoishe Pippik's user avatar
4 votes
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Turning of a paddle wheel when exposed to light

Not the complete answer, but a short analysis of expectable forces: The energy and momentum of light are related by equation $E=p \cdot c $. Then force caused by light $F=\frac{\mathrm{d}p}{\mathrm{d}...
Poutnik's user avatar
  • 42.4k
4 votes

Is light energy defined as work in thermodynamics?

Absorbing a photon will increase the potential energy of a molecule, and possibly a little kinetic energy change if rotational and vibrational energy is changed in the process. The translational ...
porphyrin's user avatar
  • 30.7k
3 votes

How to Combine an Emission spectrum into a colour?

As I understand your issue, you need to convert spectra into RGB triplets. Quantitative colorimetry theory addressing that issue is quite thoroughly stated in this wikipedia article on CIE 1931 color ...
Nicolas Peron's user avatar
3 votes
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Colour due to transmission and reflection

Since your experimental observation with copper salts negates your original hypothesis, it implies that the way you are trying to explain it is wrong. The main culprit and the source of all these ...
ACR's user avatar
  • 41.2k
3 votes
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example of endothermic luminescence?

After some digging around on Google Scholar, I came across the following article: https://pubs.acs.org/doi/abs/10.1021/ja00499a052 which presents the following class of reactions: All of these ...
creillyucla's user avatar
3 votes
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Photodissociated iodine laser and population inversion

You are making a chemical laser. A laser depend on keeping a positive difference in population between the two levels involved (upper >lower), and of course feedback for a laser oscillator. It does ...
porphyrin's user avatar
  • 30.7k
3 votes
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Does electron emit photon when it moves?

Electrons bound in atoms and molecules emit a photon at change of their quantum-allowed energy level, saving the total energy, momentum and angular momentum. Free electrons emit photons, if they are ...
Poutnik's user avatar
  • 42.4k
3 votes

Cause of continuous spectral lines

Natural white light had continuous spectrum, as the source - black radiator - has continuous emission in all wavelengths. Atoms emit or absorb only at the wavelengths, that are corresponding to ...
Poutnik's user avatar
  • 42.4k
3 votes

Difference between flame test and ability to show photoelectric effect

I think you have a misconception. Observing an emission spectrum and photoelectric effects are different things. Photoelectric effect requires not only the electron is ejected with some kinetic energy,...
ACR's user avatar
  • 41.2k
3 votes

How to Combine an Emission spectrum into a colour?

In other words, how does the eye combine the mess of an emission spectrum into a single colour? Although your query is related to vision and others have addressed it, let me clarify a couple of ...
ACR's user avatar
  • 41.2k
3 votes

How does molecular structure contribute in the property of fluorescence?

The fluorescence yield is $\varphi =k_k/(k_f+k_n)$ where $k_f$ is the rate constant for fluorescence and $k_n$ that for non-radiative processes. If $k_n \gg k_f$ then the fluorescence yield dis very ...
porphyrin's user avatar
  • 30.7k
2 votes
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What causes the blackening of light bulbs

A 14 page article (https://www.jstage.jst.go.jp/article/jieij1917/6/4/6_4_398/_article) describes the blackening of incandescent light bulbs as being totally due to evaporation of the filament. ...
James Gaidis's user avatar
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2 votes
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Process of transferring kinetic energy in regard to photons.

You may be experiencing a very common misconception, which I blame on Star Trek and Star Wars and all their talk of pure energy that always comes as bright lights, with the implicit assumption that ...
Christopher Grayce's user avatar
2 votes

Which ceramic-like material is used in halogen MR16, GU5.3 and so on bulbs?

Actually, aside from heat resistance, a primary qualification is that the adhesive cement thermal expansion coefficient match that of the quartz (or glass or alumina) envelope over the temperature ...
DrMoishe Pippik's user avatar

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