Questions tagged [light]

Photons and electromagnetic radiation, primarily in the human-visible range. For the chemical effects of light, use [photochemistry].

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Calculate frequency dose from different light intensities

The quantum yield for homolytic O-O cleavage of (CH$_3$)$_3$COOC(CH$_3$)$_3$ at $266$ nm is $0.21$. In one experiment, a pulsed laser of this wavelength was used to induce the formation of t-butoxyl ...
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How does molecular structure contribute in the property of fluorescence?

Fluorescence is the property which is exhibited when electrons emit wavelength of light lower than the one they absorbed so does that mean we can make every molecule to become fluorescent? I wanted to ...
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Why Lambert's law does not hold for photoresistors?

Why don't photoresistors made of Si obey Lambert's cosine law? Is it related to the dark current of the photoresistor? I couldn't find any solution while searching the web.
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2 answers
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A good lab demonstration of this particular optical transform pair?

At about 1:11 the video linked below shows what think is the optical Fourier transform of a sine wave as approximated by a saw blade. https://www.youtube.com/watch?v=jzmqeRp_tmk The set-up appears to ...
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How would I find what specific wavelength I need to measure for a specific chemical in spectrophotometry (calcium perchlorate)?

I am currently doing a research project, and for it, I would like to use a photospectrometer to find the concentration of Calcium Perchlorate in my sample solutions. My current method of data ...
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3 votes
3 answers
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How to Combine an Emission spectrum into a colour? [closed]

I am trying to wrap my head around the flame test, and for the most part, it is making sense. My question is their a way to figure out the colour of a flame of an unknown element given the emission ...
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2 answers
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Why does calcium emit circularly polarized light?

One page 31 of Quantum Metrology, Imaging, and Communication by Simon, Jaeger and Sergienko, the authors state that: ... calcium has two electrons in its outermost, partially filled shell; these ...
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example of endothermic luminescence?

Someone posed an interesting question to me the other day: is all production of light accompanied by the generation of heat? I have found that the question as posed invites vague answers, so I thought ...
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Can polarizing film reflect light instead of blocking light?

I was thinking about how to electorally switch glass between transparent and reflective just out of curiosity. I thought that maybe you could polarize the reflective glass in the vertical direction ...
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1 answer
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Fluorochrome (fluorescein) emission decay when linked to macromolecule

I measure the intensity and polarization of light emitted from a blood sample that contains excited fluorescein (experiment known as fluorescence polarization assay). The excitation is done, as usual, ...
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What is the amount of UV light required to make fluorophores glow and what is the minimum amount of electricity needed to achieve this?

So I have heard that fluorophores glow under UV light, so I was wondering what is the minimum amount of UV light needed to make the fluorophores glow and what would be the minimum amount of ...
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Does all fire only emit light on its outermost shell?

This question is about light emission, which may overlap with physics, but I am most interested in combustion and types of flame (incandescence, petrochemical fuel flames, nuclear ractions). Consider ...
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Does electron emit photon when it moves? [closed]

When the photoelectric effect happens or blackbody radiation happens or when an electron jumps from a ground to an excited state, we say light is emitted by electron. Now, light is made up of photons. ...
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Which ceramic-like material is used in halogen MR16, GU5.3 and so on bulbs?

I hope this question belongs in here; I cannot think of any other better place to ask it. Which kind of material is used in dichroic halogen bulbs to attach the bulb itself to the reflector and keep ...
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1 answer
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Photodissociated iodine laser and population inversion

Iodine molecules ($\ce{I2}$) can absorb in the visible region and dissociate into $\ce{2 I^.}$ radicals. One of the I atoms is in ground electronic state $\mathrm{^2P_{3/2}}$ and the other I atom is ...
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Relation of Energy required to change an orbit by electron of H atom with spectrum

We have the value for expression of line spectrum of hydrogen. $\Delta E = 13.6 \cdot Z^2 \cdot \left( \frac{1}{n_1^2} - \frac{1}{n_2^2} \right)$ Amount of energy required by electron to change its ...
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Excitation states of neon (or other gas) inside neon lights

I'm interested in the spectra of gas discharge tubes. Taking neon as an example, when I look up on NIST the spectra for neon, I find excitation states up to Ne IX. Where do I find/how do I work out ...
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How does Mars rover Curiosity's ChemCam's infrared laser produce a 100,000 K plasma plume (kT = 8.6 eV)?

Mars rover Curiosity's ChemCam uses a pulsed diode-pumped solid-state laser (DPSS) at 1064 nm to excite material on the surfaces of rocks up to 7 meters away, and a large aperture telescope to collect ...
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Actual color of colloids [closed]

I have read that the color of colloid depends upon the wavelength of light scattered by the dispersed phase and also in the sense in which the receiver receives the light. If all of this depends on ...
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1 answer
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Colour due to transmission and reflection

It makes sense to me that when looking through a sample (observer | sample | light), it should appear as the opposite of the light absorbed, but it does not make sense to me to expect the same when ...
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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? [closed]

I am just learning some chemistry after a long time without studying it and I have thought about something. Some copper compounds emit green light when heated to flame. So, I would like to know if it ...
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1 answer
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Difference between flame test and ability to show photoelectric effect [closed]

My textbook says magnesium doesn't give flame test. But it also says that it is a good photoelectric material. Are both concepts using "visible" light to remove or excite electrons? What is ...
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1 answer
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Turning of a paddle wheel when exposed to light

So, we observe that in the discharge tube experiment when a very light paddle wheel is placed in the path of cathode rays, it starts turning due to the particle nature of the rays. My question is if ...
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Predicting color of a TMB derivative affected by peroxidase

The ELISA test on HIV works by verifying the presence of peroxidase within samples. The verification process is done through the enzymatic reaction that said peroxidase has on TMB (3,3',5,5'-...
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Working principle of Fisher-Price Light Sketcher

I was just searching around in my store room and I found this Fisher-Price Light Sketcher. I am just amazed how the light from the pen draws on the board without even contact! I searched a lot but ...
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What effect does the dye color have on the kinetics of a commercial lightstick?

According to thoughtco: If fluorescent dyes weren't put in glow sticks, you wouldn't see any light at all. This is because the energy produced is usually invisible ultraviolet light. Fluorescent dyes ...
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16 votes
2 answers
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How were x-ray diffraction patterns deciphered before computers?

I know the general idea behind x-ray crystallography is to take a high quality crystal and place it in the path of an x-ray beam. Areas of high electron density will diffract the beam and lead to ...
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2 votes
1 answer
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What gives rise to the color of sapphires?

Here is what I know: Sapphires are composed primarily of $\ce{Al2O3}$ (in pure form colorless) as well as Fe and Ti (trace impurities responsible for the color). I know that the proportion and ...
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Absorption of UV Light and what color would be seen?

I am mathematically experimenting with different wavelengths of light that a fictional material would absorb. I thought of a material that absorbs a wavelength of $\pu{193 nm}$. This wavelength ...
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8 votes
1 answer
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What causes the blackening of light bulbs

in 1878, Thomas Edison (or rather William Joseph Hammer) added an anode in a light bulb in order to catch the flux of electrons coming out from the carbon filament and reduce the phenomenon of ...
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1 answer
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What molecules are produced in carbon arc lamp and how do they produce light?

I am curious about the chemistry of the arc lamp (an indirectly for the incandescent bulbs) thus I would like to ask the following. It is a common understanding that the electrons pushed inside an ...
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3 votes
2 answers
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Cause of continuous spectral lines [closed]

We know different types of atoms have different spectral lines. But what exactly are the spectral lines representing? What causes white light to have a continuous spectra while other atoms show ...
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28 votes
2 answers
7k views

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

Totally an elementary question. Staring at a candle, it appears that the bottom of the wick is dark whereas the top glows. However the bottom of the flame (the blue) is the hottest. Is the reason ...
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2 votes
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How do we determine the proportions of hydrogen to helium (to other elements) that make up the Sun given the absorption spectra?

I am reading about the composition of the Sun and how it is made up of mostly hydrogen (~90%) and helium (>10%) and other elements with much smaller quantities. The explains that different elements ...
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Photochromism time of colour change

I know there are chemical pigments/dyes which produce an immediate reversible colour change in UV or direct sunlight. Is there a way to postpone the colour change so that it does not happen ...
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1 vote
1 answer
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How to assess sunscreen effective via blueprinting?

How do I assess the effectiveness of sunscreen creams by using the blueprinting process? I know blueprinting is done when something is sensitive to light and this may cause reactions to produce a ...
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2 votes
2 answers
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Directional emission from molecules

This might be a silly question (probably is). When a molecule absorbs it has a transition dipole moment, a measure of how strongly a certain transition will interact with light will depend on how ...
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2 answers
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Process of transferring kinetic energy in regard to photons. [closed]

Now I know that temperature is the average kinetic energy of atoms, molecules and compounds. Photons increase the kinetic energy/temperature of molecules since photons are pure energy. Hence, wouldn't ...
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-1 votes
1 answer
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How much heat is created by absorbent-type sunscreens?

I have a friend who claims her dermatologist told her than sunscreen was what was burning her skin. (I think it's much more likely that her rash/burn was either a sunburn, a skin reaction to some ...
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5 votes
1 answer
686 views

Why objects usually don't exibit fluorescence/phosphorescence?

We learn in school that the color we perceive is determined by the light that is reflected back at us. Not all wavelengths of light reflect back at our eyes, some wavelengths are absorbed. I'm ...
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4 votes
2 answers
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Will borosilicate glass absorb 808nm laser light?

Will borosilicate glass absorb 808nm laser light? If it instead refracts, then what is the refractive index? Also, will borosilicate reflect lower frequencies of light like those used in non contact ...
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