Colin K
  • Member for 11 years, 1 month
  • Last seen more than 4 years ago
How can airplanes fly upside down?
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41 votes

Upside-down or right side up, flight works the same way. As you stated, the wing deflects air downward. When inverted, the pilot simply controls the the pitch of the aircraft to keep the nose up, thus ...

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Are human eyes the best possible camera?
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35 votes

This question is sort of difficult to answer in an objective way, because it depends very strongly on your definition of "best." Natural selection favors traits which provide a reproductive advantage; ...

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What makes some laser beams visible and other laser beams invisible?
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32 votes

As previous answers have stated, the wavelength (or frequency) and intensity of the beam are important, as well as the type and amount of impurities in the air. The beam must be of a wavelength that ...

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Newton's rings: What causes the other rings?
24 votes

This is a manifestation of "Frequency Aliasing" which shows up in lots of situations where you have data which is sampled at discrete intervals. For a more in-depth explanation of aliasing in general, ...

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Does it contradict special relativity that an electron beam in a television picture tube can move across the screen faster than the speed of light?
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20 votes

This is an example of what is sometimes called the "Marquee Effect." Think of the light bulbs surrounding an old-fashioned movie theater marquee, where the light bulbs turn on in sequence to produce ...

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Interference of polarized light
16 votes

Yes. In fact, light will only interfere with light of the same polarization. If you take a Mach–Zehnder interferometer, for example, and put a polarization rotating optic (a waveplate) in one of the ...

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Aspherical lenses - perfect analytical shape
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15 votes

The last part of your question is the easiest to answer, so I'll get to that first. The best book on the fundamentals of optical design is "Modern Optical Engineering" by Warren J. Smith. It is not ...

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Optical explanation of images of stars?
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14 votes

This is, as Lubos mentioned, an effect of the wave nature of light, and cannot be explained using geometrical optics. What you are seeing is called the Point Spread Function (PSF) of the imaging ...

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Helicopter in an Elevator
12 votes

The air in an elevator does tend to move with the elevator, because it has relatively little inertia. However, thinking about the problem in these terms seems, to me, misleading. The simplest way to ...

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Are electromagnetic "plane" waves measurable or just a virtual concept?
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12 votes

A "plane wave" generally refers to an infinite and perfectly flat wavefront, which cannot exist in reality, of course. However, there is nothing at all impossible about a plane wave of finite extent. ...

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Cladding of optical fibers
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12 votes

For a fiber to guide light, even considering the situation using only geometrical optics, there must be total internal reflection (TIR) at the boundary of the fiber core. For TIR to occur, the angle ...

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What is so good about diffractive optics?
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11 votes

Diffractive optics aren't magic, they are simply another tool that can be used in designing an optical system. They can do things that refractive optics cannot, and they are often lighter and smaller ...

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Where does the energy go, when light is blocked by polarisation
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11 votes

It is possible to "block" light based on its polarization in a number of ways. In the situation you are describing, where the light hits a polarizing filter, it is simply absorbed by the filter. The ...

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Do high/low pass lenses exist?
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11 votes

There are many ways to do this. Which option you choose depends on what degree of performance you require, and how much money you re willing to spend. First of all, you should understand that, while ...

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How does Fraunhofer diffraction depend on the orientation of the sides of a lens?
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10 votes

Background As has been stated in the answer you linked to, the propagation of light from the pupil of an imaging system to the image plane can be modeled by a very close approximation called ...

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Why is it difficult to differentiate between interference and diffraction?
9 votes

It's difficult to differentiate between the two phenomena because they are fundamentally the same phenomenon. It's common to use the term "interference" in a more general sense, where the interfering ...

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Optics of the eye - do we see Fourier transforms?
7 votes

As mentioned in the question, a thin lens will produce in its focal plane the Fourier transform of the optical field in its pupil, possibly multiplied by a quadratic phase term. However, to understand ...

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What longest time ever was achieved at holding light in a closed volume?
7 votes

The lifetime of a photon in a resonant cavity is pretty trivial to compute, given the cavity length, internal losses, and mirror reflectivity. Switching momentarily to a wave description, we will let $...

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How to interpret the appearance of time units in the units of a physical quantity?
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7 votes

Units don't always have intuitive meaning, particularly when you reformulate them in various ways. The pascal is intuitive when you express it as force/area, but you can reformulate that in dozens of ...

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What is the physical reason a $+5V$ equipotential coutour cannot intersect a $-5V$ equipotential coutour?
7 votes

While it may be possible to derive a violation of energy conservation due to intersecting equipotentials, there is a much more intuitive and in my opinion a more fundamental reason that equipotentials ...

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A telescope with a bunch of small mirrors
7 votes

The telescope you describe would work in some sense, but it depends strongly on how you define what it means for a telescope to work. Combining many mirrors to behave as a single large mirror is ...

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Whats the range of dimension exponents in the SI system of units?
7 votes

At least one common quantity I can think of has dimension with a non-integer exponent. The specific detectivity, $\text{D}^*$ is a common descriptor of photodiodes, and I'm sure one could make an ...

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"Optically performed" Fourier Transform
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7 votes

EDIT: Upon reading the question, I leapt to the conclusion that the asker was curious about the Fourier transforming properties of lenses. I am embarrassed to say that I did not immediately read the ...

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Material resistency to lasers beam
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7 votes

Typically, a laser will damage an optical surface in one of two ways. The first is just what you would expect: the laser heats the material up until something bad happens. The second is also pretty ...

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Why are volume and pressure inversely proportional to each other?
6 votes

Pressure and volume have an inverse relationship when $n$ and $T$ are constant. How do you imagine the pressure in the balloon is increased? Either $n$ or $T$ must increase, or $V$ must decrease. ...

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Is it humanly possible to change Earth's axis?
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6 votes

Inertia does not suddenly "break" in the sense that the axis will remain fixed until some force threshold is reached, and move thereafter (for that matter, an ice skater cannot change direction by any ...

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why isn't the variance of Fano noise proportional to the number of photon arrivals?
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6 votes

It seems that the confusion is due to some unfortunate notation. As the OP states, Fano noise is due to the variance in photoelectron production per incident photon, and this should indeed be signal-...

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What causes compressed air (from "Dust Off" cans) to freeze, but only when turned upside down?
6 votes

The fluorocarbon in the can is a liquid under pressure. When you spray the can upright, only the fluorocarbon vapor at the top of the can is released. When you turn the can upside-down, the liquid is ...

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How does carbon dioxide or water vapour absorb thermal infra red radiation from the sun?
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6 votes

As you can see on these absorption spectra for $\textrm{H}_2\textrm{O}$ and $\textrm{C}\textrm{O}_2$, both molecules have moderate to strong absorbtion in the mid-IR wavelengths, with the absorption ...

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What means: distortion <XX% in lens spec?
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5 votes

Distortion is a magnification which varies with field angle. Given as a percentage, it describes the image height of an object at the edge of the field, relative to the height it would have without ...

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