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1

This is not thin-film interference, which involves waves of light interfering. You're looking for a Moiré pattern. This sort of phenomenon is difficult to model analytically, since it involves step functions with varying offsets. Perhaps surprisingly, your eyes play an important role in this. Your receptors are arranged in a rough-Poisson-disk ...

0

If you think about it, a pulse that is much narrower than one pulse of the "center frequency" is really no longer related to that center frequency and just becomes a delta function. If you just take the Fourier Transform of the pulse shape, you end up with the actual frequency components - an essentially flat response. The "negative frequencies problem" you ...

0

The parallel rays which are away from the principal axis and not meet at the principal focus after reflection are called marginal rays. AND The parallel rays near to the principal axis and after reflection meet at the principal focus are called paraxial rays.

7

I am going to answer this on the assumption you are talking about an incandescent lamp. A tungsten filament is heated by the current flowing through it, and starts to behave like a black body radiator. Now a tungsten filament is not a perfect black body: the emissivity is a function of wavelength and has been characterized (see ...

10

For starters, even though you don't say it explicitly, I'm going to assume you're talking about incandescent light bulbs (since you mention filaments in your question). There are many other types of light bulbs, such as compact fluorescent lamp (CFL) or light-emiting diodes (LED). Each of these different types work somewhat differently, and as a result, ...

18

If it is incandescent, then temperature to some extent, but mostly the light of the wrong color gets filtered out by the colored glass bulb. If it is something like electric discharge lamps, then it is the gas used (eg sodium vapor) or the phosphors coating the inside of the tube converting UV to visible light/color (eg mercury vapor UV emissions). With LED ...

0

There are a couple of things here to clarify. What is darkness, just (a shade of) black color (as per @anna's answer), yes a machine can do that. Is it a about a machine that outputs passive darkness (as per @DavidZ's answer), yes it can be done (just dont output anything, it outputs darkness). Is it about active darkness in the sense that it can ...

5

You speak of fading over seconds. This is not likely to be a result of filament glow in a mains voltage domestic light as they cool very fast. There is unlikely to a sodium vapour lamp in your bathroom either. Most LED lights will turn on and off pretty fast as storage capacitors are expensive to waste. Possibly a thick filament (low voltage) halogen ...

1

I'd like to add to Chris White's excellent answer and summarise things thus: $c$ is a number that parameterises the family of all possible linear transformations that follows from Galileo's relativity with the assumption of absolute time relaxed. If you do Galileo's relativity with the assumption of an absolute time (that two relatively moving ...

6

Long ago, English speaking sailors measured horizontal distances in units of nautical miles but depths in units of fathoms. The distance in fathoms to some point $z$ fathoms deep and $x$ nautical miles along the surface is $d^2 = 1012.68591^2 x^2 + z^2$. There's nothing physical to that factor of 1012.68591. It's solely a result of using inconsistent units ...

5

The quantity $c$ is a very fundamental constant related to space and time. It is largely independent of the existence of matter or light or any other substance. It is probably more ontologically appropriate (if not pedagogically appropriate) to define it as the number that makes Lorentz transformations between reference frames work. The quantity $c$ would ...

3

This is a very complicated question and a complete answer would be very deep and very, very long. Much of it stems from the fact that the speed of light is independent of the frame of reference from which it is being observed. In this sense, it is one of few "universal constants" - that is, quantities which do not depend on the observer. Since it has units ...

2

Cosmology usually adopts something called the "Cosmological Principle", which is that, on large scales. the universe is homogeneous and isotropic. Therefore the universe looks the same wherever you are and looks the same in all directions. Thus light emitted from our part of the universe travels outwards and is received by distant parts of the universe ...

-1

If this is so, then isn't light constantly getting past all matter in the universe and so being lost. It may be, but we have no way to know. We do not see far enough to see what happens on the edge of the material universe. Even if there is such edge and only vacuum beyond, energy of the material universe does not need to decrease, because there may ...

2

If you reduce the intensity of the light beam so that effectively you know you only have one photon in the apparatus at a time, then what is observed will depend how it is observed. In all cases though, the detected light (photons) will have the same frequency. If you set up a detector so that it records the arrival of photons (note, you cannot have half a ...

-1

When photon hit the surface of the metal they transfer their energy to the metal free electrons. When metal electron get the higher frequency near about to that of light they emit another kind of light. Rishabh raj mishra

0

We can never actually emit darkness, its physically impossible from the current knowledge of physics. To elaborate upon that answer, normally when humans look with their eyes they see the visible spectrum and therefore we cannot see any more or less frequency than that, this therefore results in us either not being able to see it in its true form. Now, ...

-1

Like The great sir Albert Einstein said to his dumb teacher- " there is no coldness its only the absence of heat ". Analogously we can say that there is nothing such as darkness its just the absence of light . But wait a minute Young's double slit experiment proves that light + light =light and light + light = darkness as well. It's not possible to create ...

3

You said that the lamp gave off a yellow glow, so it is possible that it could be a sodium lamp. However, your conception about light intensity and wavelength is a bit off. If the lamp that you are speaking of gives off a monochromatic light source, it is most likely using an electrical current to excite the atoms of a single element. When excited, ...

4

"Relativistic" velocities (velocities in excess of 0.1 c) are not needed. Any velocity difference will do. People use the doppler effect right here on Earth. Some sample uses: Catching speeders. How fast is his fastball? (Very important at this time of year.) Where is that tornado going?

0

Your choice of the word "notice" is ill-defined. The Doppler effect holds true for all waves, at all speeds, so in that sense, you could "notice" the Doppler Effect for any wave you choose, no matter what the speed of the source or observer is (as long as there is some relative motion between the two.) Even as you walk across a room towards a lamp (to keep ...

2

As you clearly ask for a detection criterion of the doppler shift on "a sample light wave", I have taken the liberty of assuming the following scenario. You detect light from a source, emitting light of a known wavelength (the usual case in astronomy for instance) with an instrument that is capable of measuring wavelength with an accuracy (i.e. with an ...

1

Everything scattering light has a characteristic spectrum. The spectrum is defined by the way wherein the particular thing interacts with light, and this is set by the (1) chemical makeup and (2) texture (at the wavelength-of-visible light scale). You cannot change the spectrum without changing one of these two things, either by e.g. (1) altering the ...

1

Many light bulbs already do this. See for example this article. I was in the lighting technology business at one point. At that time it was done in some tungsten-halogen incandescents. I don't know current state of things.

0

As CuriousOne says, look carefully for a test suite within your software installation. MEEP is widespread, notwithstanding the LISP interface (gotta love MIT's confidence in its own creations), so if you seek carefully, you are bound to find MEEP analysed examples on the web. As for your proposed simple test: it is a good idea, and there are many, well ...

8

Interesting question! Cherenkov radiation would definitely be inefficient for illumination. You only get Cherenkov radiation from charged particles moving faster than the local speed of light in a medium. If you have a transparent medium with index of refraction $n=2$ and you're sending fast electrons through it, you'll only get Cherenkov radiation while ...

4

Quite aside from the issue of ionizing radiation, Cerenkov generating particles also lose energy by other processes and that ends up as heat. Moreover, all the kinetic energy of the particles once they drop below the Cerenkov threshold is lost in non-optical channels (i.e. more heat). So no, they could never be anywhere near as efficient as diode ...

1

Better late than never? Yes, what you found in the Matlab package is correct. The luminosity function is the exactly the same curve as the green part of the three XYZ Tristimulus Curves used in modeling human perception of color. Note the XYZ color space is not the same as the RGB color space of a display; XYZ represents the totality of what humans can ...

0

You are totally right about photons and their reflection and absorption on bright or dark surfaces if you illuminate these surfaces with visible light. The photons in the range of visible light will be reflected or absorbed (and re-emitted with a longer wavelength) and that is the reason we see these surfaces as bright or as dark. And the dark surface has a ...

0

When I was in high school I wondered the same thing. According to the Inflation models space time expanded exponentially between $10^{-36}$ and $10^{-32}$ seconds after the Big Bang. According to the theory a piece of space the size of a nucleus expanded to the size of a galaxy (rough order of magnitude, possibly even larger) in that very short time. ...

0

For a parabolic mirror, the answer is "all rays go through the focus". For a spherical mirror, you can see the answer most easily by looking at the limit as the spherical mirror is almost a hemisphere: Clearly the rays that start further off axis are focused closer to the mirror.

1

Unfortunately, as interesting an idea as this is, and as creative as you must be for thinking of it, it's not an actual possibility as far as I'm concerned. A one-way mirror works much in the same way that a metallic screen door works. It allows you to see from the inside of your house, outward. However, this is due to the fact that there is far more ...

2

In addition to @Floris response: You have missed a lot of wavelengths in your list of wavelengths that would experience interference. Take your example of a $6,000,000 \text{ nanometer}$ pane of glass, and consider that 15,000 waves of $400 \text{ nanometer}$ wavelength light exactly fills this space. So, indeed, this light will experience some sort of ...

3

Very simply, when a plate is quite thick, the fringe patterns will be very close together - because a tiny change in angle will result in an additional wavelength's worth of path difference. Different colors will have a different repeat distance (because of different wavelengths); and light will typically arrive at the eye from more than one direction ...

0

The answer I gave before was wrong, as was kindly pointed out by CuriousOne. The fading of the intensity isn't because of the $1/r^2$ fall-off of light, since the diffraction formulas are only for small angles anyway. First of all, it's clear from the second figure in the question that the only relevant thing is the diffraction and not the interference; ...

0

Is this not a question about human physiology rather than physics? We are discussing the variations in observed response of the human eye to light with different qualities: overall intensity, and distributions over the visible spectrum. This question seems to ascribe all of the observed differences (or lack thereof) to the quality of the light; "the Moon ...

1

But I've never seen that happen. You haven't looked then. The rising or setting Moon is rather reddish, just as is the rising or setting Sun. However, there is a difference between the Moon and the Sun. You can look directly at the Moon, even a full Moon, regardless of where it is in the sky. On the other hand, you can only glance at the Sun when it is ...

2

This is just an opinion, but the moon on the horizon is simply less visible than the sun is. I suspect that color changes it makes are more subtle and less easily noticed. However full moons are often noticeably orange. Here is a page with a wonderful time lapse view. http://www.pikespeakphoto.com/moon-rising.html

1

Reflection,refraction and transmission of light are macroscopic manifestation of a phenomenon called scattering.In this incoming photons are absorbed and either the quantum energy level of an atom is raised (as in case of resonance absorption) or the outer electron cloud is set into motion(this is responsible for light around us).Almost instantaneously ...

1

The spot of light isn't below the line of sight of the laser gun, and the outside observer shouldn't expect that to be the case. The laser gun is attached to the elevator wall, so according to the outside observer, the momentum of photons as they come out of the laser gun must have a non-zero upward component, or else conservation of momentum would be ...

0

If the elevator is going up rather fast, the light from the back of the elevator takes longer to reach the observer than the light from the front. This means that I see the back of the elevator at an "earlier time" - put differently, it looks to be a bit lower. The angle by which it appears to be lower is given by the velocity of the elevator divided by the ...

0

Neither the antumbra nor pentumbra have a fixed brightness. It varies across the region based on the amount of the solar disk that is visible. Each has regions where it is brighter than places in the other. It does not make sense to call one "brighter" than the other.

0

I'm going do do the annoying teacher thing where I answer a question with a question. Which is darker, a partial solar eclipse, in the penumbra of the moon, or a planetary transit, in the antumbra of an interior planet?

-1

In the penumbral area, part of the disc of the moon obscures a section of the sun. In the antumbral area, the entire disc of the moon obscures a, logically, larger section of the sun. Therefore the antumbra cannot be brighter than the penumbra during the same event.

4

Your eye has a lens in it. Without a lens, the light is all spread out and overlapping, just like you say. The light from any given pixel goes out in all directions, but a lens can make it re-converge back to a point. Hold up a sheet of white paper. Is there an image on it? No, of course not. It has light on it---light coming from each object in the ...

2

Let me go a little further than @mark-h's answer: The behavior of light at an interface is described by the electro-magnetic field solution to the Helmhotlz equation. It gives the reflected and transmitted electric and magnetic components as a function of the refractive indices of the incident and exiting media. From those solutions we can derive the ...

0

The small angle approximation is very reasonable here. The angle of deflection predicted by the approximation is ${4GM \over rc^2}=8.49\times10^{-6}$ radians. Writing $\tan{\theta}$ instead of $\theta$ is just clutter. The difference between the two is $2.039\times10^{-16}$. In order to resolve this difference in angle in visible light, you would need a ...

6

To follow the information in Chris White's answer - essentially, you would want a medium that allows you to see the spectra. There are several online resources that could help you in this experiment, in particular, the CD spectrometer, which can be constructed simply and on that website, it shows several examples of how everyday light sources can be ...

9

Lasers by definition only emit a single wavelength of light. You use one if you want that wavelength or if you want your photons to be in phase. You don't care about the photon phases, and you want to sample all wavelengths, so a laser is very much the wrong tool. If you just want collimation of the light, mirrors, lenses, or even just well-separated ...

1

Binocular vision has already been discussed, but it left out an important aspect. A single eye is sensitive to distance. The shape of the lens changes to focus on near/far objects. The reason this is needed is that our pupil has finite size and cannot be modeled as a pinhole. The same physics is going on here as in a lens of a camera focusing on an ...

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