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4

In general it is not possible to tell, because some colours simply cannot be assigned a definite wavelength. Some colours, like green or blue, have essentially unique combinations of wavelengths that produce the (subjective) impression of green or blue. Some colours, like yellow, can be produced in multiple ways: light of 580 nm will look yellow but so will ...

1

It will be difficult to arbitrate. Usually green color wavelength varies from $510*10^{-9}$ to $560*10^{-9}$ $m$, most commonly it is assumed $520*10^{-9}$ $m$. Blue color wavelength varies from $450*10^{-9}$ to $495*10^ {-9}$ $m$, most commonly it is assumed $475*10^{-9}$ $m$. Turquoise color is difficult to define, most commonly it is said to be a ...

1

Refraction causes the shift to shorter wavelength, but scattering causes the shortest wavelengths to usually not be observed, as explained by astronomer Andrew Young here. In rare instances the flash can be blue, as seen in these photographs at Atmospheric Optics.

0

If the bulb was a perfect diffuser, each point on the light bulb would scatter all the light that struck it uniformly over a hemisphere. The surface of the bulb would appear uniformly bright. This would be the simplest assumption. If the bulb was perfectly clear, there would be no scattering. Light would travel in a straight line from the filament. The ...

0

Since you can chose the bulb, chose something convenient. The spectrum of Flourescent and white LED bulbs depend on the phosphors used, which can vary considerably between models and may be hard to find specs for. I'd chose incandescent because those are basically just black body radiators. Pick a plausible color temperature for a incandescent bulb and ...

1

The Lorentz transformation gives the relationship between the time and space coordinates of two inertial reference frames in relative motion. As such, it is coordinate length contraction and coordinate time dilation that results. Thus, in SR, observing (or measuring) length contraction does not mean to photograph length contraction. Rather, it means ...

0

Well, trying to get in the form of what Mark Wayne put down...you can start with the dfinition of the energy density "u" and find the partial wrt time. From there you can use Maxwell's Equations to make some substitutions. Finally in the end you will NEED a not so known/popular vector identity to give you the (ExB) term. Good luck...not a bad derivation at ...

1

One simple model of a diffusive material is a material where there is a certain probabability per path length that a photon will be scattered in a random direction, similar to how a colored material absorbs photons with a certain probability per path length. If the characteristic length of the material is $L=d^{-1}$, where $d$ is a "diffusivity factor" for ...

1

In interference and diffraction, light energy is redistributed. If it reduces in one region, producing a dark fringe, it increases in another region, producing a bright fringe. There is no gain or loss of energy, which is consistent with the principle of conservation of energy. If you consider a point where there is destructive interference, there is a dark ...

2

You are right that the sun appears to emit a continuous spectrum, and that's due to the fact that it's a black body to reasonable approximation. We don't even have to consider the spectral response of our eyes, or the color mixing in our brains. Measurements with 'cameras' of one type or another are routinely made to produce plots like this. Discrete ...

1

In theory, there are not any disallowed wavelengths from a perfect blackbody. In practice, at the current resolution, spectra that have been observed in nature do not show any gaps. There are absorption and emission lines on most spectrum, of course, but they are due to deviations from black body idealizations, such as gas in front (or within) of the light ...

0

Actually, total internal reflection is impossible in spherical raindrops; an internal reflection occurs, but it is not total. And the rainbow is not just an arc, it is a full disk. The disks are sized differently for each color, and are brightest at the very edge, which is what makes the colored arcs appear. For the primary rainbow, these disks are centered ...

1

An excited state electron may transition to any lower level. From n=4, the electon could go to n=3, n=2 or n=1. Of these 3 transitions, only n=4 to n=2 (wavelength 486nm) is visible light. n=4 to n=1 is ultraviolet and n=4 to n=3 is infrared. The wavelengths of the transitions are given by the Rydberg formula. ...

4

I would make a flag from iron oxide (red), platinum (white), and lazurite (blue). It won't wave in the wind, but it will retain the color. The base would be a platinum plate, of course. I would made a really large one, so that people wouldn't complain that it was too cheap.

1

Yes. Every object whose temperature is not 0 K radiates. That means that every object glows in a sense. For everyday objects at everyday temperatures, the wavelength of the glow is around $10\, \mu m$, far in the infrared, and far outside the range of human vision. As you heat the object, the wavelength of the radiation gets closer and closer to the ...

24

The Apollo 11 flag was included almost as an afterthought. It was just a month or so before liftoff, and someone at NASA slapped themselves on the head and said, "we need an American flag to plant at the landing site!" Someone rushed out to a local store (Sears?) and bought a standard nylon flag, which went to the Moon. Besides being bleached out by solar ...

15

Yes, there are. Such materials are called "saturable absorbers," and are (or at least, have been) used as switches in some laser designs. The one I recall is a nickel acetate dye, although there are others. Basically, the molecules absorb single photons at the laser wavelength, but when the intensity is great enough that two photons are absorbed ...

1

in welding a plasma is created, it's a mix of ions, electrons and atoms. alltogether they are a neutral mix. once you get plasma you get a ton of UV coming out of it, very dangerous to eyes not only on the direct contact, but also via reflection from other objects. in your case, I still don't know what exactly is the device you are creating. It sounds like ...

2

All materials emit thermal radiation (such as light). The hotter the material, the more the radiation is shifted to high frequencies (shorter wavelengths). The radiation comes from oscillating electrons (regardless of whether there is an electric current). Welding reaches temperatures high enough to cause significant emission of UV light. Oxyacetylene and ...

0

Remember that you must always specify the inertial frame of the observer. Other than that, your question makes perfect sense. The "closing" velocity of the two photons approaching each other will be 2c only in an inertial (stationary) observer at rest relative to the center point. To an observer "riding" with one of the photons, (either one), the closing ...

1

Another interesting way to see this, if you live or work where you can see a mountain range, is to train a telescope to some object on top of the mountain. Not only will you see the quivverring image you speak of, if your telescope mounts are stable and you don't adjust them, you will see that the object will move up and down in the telescope from day to day ...

0

The question of what is the velocity of a photon relative to another photon does not make sense. Neither it does asking what is the velocity of anything relative to a photon. This is because in special relativity we only have the concept of a velocity defined for a massive observer, which is defined from the four-velocity $$u^\mu = \frac{d x^\mu}{d\tau}$$ ...

5

$400$ - $700\text{ nm}$ corresponds to about $430$ - $750\text{ THz}$ ($10^{12}\text{ Hz}$), not $\text{MHz}$ ($10^6\text{ Hz}$). To convert from wavelength to frequency, use $$f = \dfrac{c}{\lambda},$$ where $\lambda$ is the wavelength, $f$ is the frequency and $c$ is the speed of light. So, for $400\text{ nm}$, this is:  f = ...

0

Reflected light can be though of as originating in oscillating charges in the medium. The incident light causes the charges to oscillate, and the oscillators generate the reflected light. This process happens almost instantaneously. The atoms in the medium are oscillating coherently (in step) with the incident radiation. The frequency of the light is ...

1

Like KsdLingen said a photon does not really have a length or size. You could ague that this is due to its wave-particle duality (a concept from quantum mechanics). The wavelength of a photon, $\lambda$, indicates what distance it will travel in vacuum while its electromagnetic field completes one period. The direction of these fields are always ...

2

The wavelength of light, and for any wave in general, is measured along the direction of propagation. It has every bit of the intuitive meaning that the wavelength of a water surface wave does. One of the most meaningful ways to visualize light is as an oscillation of the electric and magnetic fields over space and time: (Image source) The electric ...

1

The 'length' is indeed measured in the direction the wave is traveling. A lightwave is a transverse wave, consisting of an electric and a magnetic field. A photon can be imagined as a localized wave. Length and shape of a photon are meaningless concepts

0

(I presume you mean resolution.) In an SEM, the limit to resolution is almost always determined by the volume over which the electron beam interacts with the sample. If you shoot a beam into a sample at several keV, electrons will bounce around within a volume of something like a micron in size (depending on the exact voltage, the density and shape of the ...

0

Actually a much more difficult question is why is glass transparent and does not SCATTER? Lack of absorption is just one explanation. But take a ceramic. It does not absorb (e.g., toilet bowl) yet it is not transparent. So why is glass transparent. This does NOT really has a trivial solution.

0

There are physical and physiological aspects of this problem. Consider this: if your fingers are freezing in cold is it better to drink a hot tea or cold vodka? Definitely VODKA! Why? because it will immediately cause your blood vessels to widen, more blood will go to your fingers and you'll have a better chance to save them. Did I make this up? No. My ...

2

This article has some relevant results based on a study of bird plumage (it also happens to be cited in the abstract of the Nature paper mentioned in one of the other answers), and is summarized in simpler terms here. I'll attempt to summarize the summary. Black and fluffy/loose fitting clothing is best if it is hot out and there is any (\$>3 ...

3

This is simply the law of reflexion: if you trace a ray diagram for objects reflecting in your iPad screen, you are looking at light from a virtual image that is as far beyond your screen as the real source of light is from the iPad screen. So if the lamp is, say, 3 metres behind your shoulder, when you look at the iPad screen the reflected light is exactly ...

0

One cannot collimate light from an LED accurately without loosing a great deal of light and / or being happy with a very wide collimated beam, because the source is often quite a wide extended source (sometimes up to 1mm across). This may or may not be a helpful answer depending on exactly what you mean by collimated, i.e. how accurately you need to ...

1

Optical systems not involving magnetic fields are symmetric. So, if the display passes light in one direction, it will pass light in the other. Putting a mirror at the back of the TFT and lighting it from the front is therefore equivalent, expect that some light will be attenuated on the way in as pointed out by @CarlWitthoft in the comments. As a ...

2

Imagine each torch gives off marbles instead of light. And instead of a light detector we use a cup. In this model, the number of marbles entering the cup per second is like brightness. If you have only one torch on, only marbles coming from that torch enter the cup. Now turn on the second torch. There will be more marbles hitting the cup every second. The ...

4

He's right. If you shine two flashlights on an object, there is twice as much light hitting it as if you used one flashlight. It's as simple as that.

-1

the resolution is kλ/NA k is a technical factor

0

When the train is moving, the light that causes the shadow actually moves in opposite direction to that of the train. When the light source is perpendicular to your direction of motion it is casting a shadow directly opposite. now, when we move little further(i.e. the screen on which the shadow appears has moved a little distance further), so the shadow of ...

2

The white colour of clouds is due to Mie scattering. This arises because the refractive index of water is different from air. If the particles are large enough all wavelengths are scattered equally so there is no change in the colour of the scattered light. This is the case in clouds where droplet sizes are typically 10 to 20 microns. The light scattering ...

1

A couple things: this site is not specifically for engineering questions, so there's a small chance this may be closed by mods. Second, many commercial high-power LED's are listed not by luminous flux, but by nominal diode power consumption; a 1 watt LED actually emits far less than 1 watt of radiant power, so you'll need to think about what radiant flux ...

2

This is effectively just a diffraction problem. I.E. you get out a diffraction pattern on the left similar to the one you expect to get on the right in the first case, and one of the peaks will be at the original light source. Why will we get multiple peaks instead of just one corresponding to our original light source? In the case of the first ...

2

This sound is most likely caused by the choke coil which is inside the lamps housing. It is needed for lamp starting and operation. Starting works like this: After initially the starter circuit allows for current flow through the heaters in the tube, it interrupts the the current after an initial period. This causes a high voltage impulse to be created by ...

1

Three guesses: Light is composed of zillions of photons, elementary particles which even though have zero mass carry momentum. p is the momentum , h is Planck's constant, c the velocity of light, nu is the frequency In the link you gave one sees that the ping sound comes at a delta function in time of a lot of light. My first guess is that the ...

4

Sure, that is what the wavy motion over a hot car is, and also the cause of mirror-like mirages on deserts and hot roads. Stars also twinkle due to the same effect. Not sure about street lights per se, but I'm sure there are combinations where air refraction of light would show up there also.

0

"In several parts of this treatise an attempt has been made to explain electromagnetic phenomena by means of mechanical action transmitted from one body to another by means of a medium occupying the space between them. The undulatory theory of light also assumes the existence of a medium. We have now to shew that the properties of the electromagnetic medium ...

3

I'm not sure I've understood your question but I think you're asking if a big wave can have wave-features on its large features. If so, sure, why not? You can add waves of different frequencies to achieve results like:

0

Besides the physiological part of optic nerve and brain, we call an object coloured if it reflects light of a specific wavelength (or wavelengths) from the complete visible spectrum. And we call light coloured if the light source only emits a part of the complete spectrum.

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