# Tag Info

204

You are getting reflections from the front (glass surface) and back (mirrored) surface, including (multiple) internal reflections: It should be obvious from this diagram that the spots will be further apart as you move to a more glancing angle of incidence. Depending on the polarization of the laser pointer, there is an angle (the Brewster angle) where you ...

178

Your brain adjusts your perception of color to compensate for lighting that is strongly tinted. This was the reason for the violent conflict some time back about a certain dress. Depending on whether people perceived the dress was being lit by yellow-tinted or blue-tinted light, they saw either a black and blue dress or a white and gold dress. Here's an ...

176

We do. Normally the reflections are too quick to hear distinctly, and in an environment like a room they rapidly become diffused into a mush which a sound engineer would call reverberation. In larger spaces you can often hear distinct echoes as well or instead: a good way to play with this is to clap your hands (once) in a quiet hall: you will hear the ...

168

Because the real situation looks a lot more like this: Your pen is (presumably) not made of mirror-like polished metal, but rather of something like wood or plastic that reflects light diffusely. This means that the light from each part of the pen is scattered all over the paper (and, of course, in other directions too), so it won't project a clear image ...

143

I believe this is what's happening: The first "beforeghost" is the faint reflection off the surface of the glass. The second solid image is the intended reflection off metalized layer. The third "afterghost" is the faint internal reflection off the inside of the glass, then properly reflected again off the metalized layer. There are actually many more "...

102

The fabric is made of many thin fibers of fabric, with air in between. This structure causes light to bounce around many times inside, making it hard for light to get through. When you make the fabric wet, you replace the air with water, which has a closer index of refraction to the fibers. So the reflections inside are less important, and more light just ...

92

You are seeing ghosting in a second surface mirror; most laser applications with mirror(s) - the good or critical ones - use what is called a first surface mirror. The other answers did explain it fairly well already but I wanted to add some terminology and a photo to help explain. Example of a second surface mirror (left) and a first surface mirror (right)....

77

Your misunderstanding is very common and quite easy to make. Basically, what students are usually introduced to first is the thermodynamics of ideal monoatomic gasses. This is good because it is simple and easy to understand, but can be problematic because features specific to the simple substance can be misunderstood as general features of all substances. ...

65

I've made this into an answer because it's too long for a comment, and I really want to show the pictures. It is tempting to think of visible light as "close enough" to (near by wavelengths) and to conclude that "yes, actually, the yellow does affect it. I want a mirror without an obvious tint" However you are wrong, Physics will slap you down. Exhibit A ...

61

The key is that light must enter the eye for you to see something. You cannot see a beam of light from a low powered laser which is not directed into your eye if the air through which the light is travelling is devoid of dust. Adding dust to the air and you can see the trajectory of the laser beam because of the light being reflected/scattered from the ...

54

If you look at the reflectivity of gold (vs silver or aluminum) you can see a plateau at wavelengths below 500 nm source: If blue wavelengths are not reflected as well as other colors, the resulting image will look "more yellow" - which is what you see. At longer wavelengths, gold is a very good reflector (better than the other two above 600 nm). It also ...

53

These are probably caused by minute, periodic variations in the diameter of the table leg, formed by drawing through a die. Any vibration in the process would end up being circumferential waves in the surface of the tube. Changes in the diameter mean changes in the slope of the surface, and thus focus the reflected light to different rings around the base of ...

52

Look at the electromagnetic spectrum: Visible frequencies have wavelengths of microns, $10^{-6}$ meters. Gamma rays have a wavelength of $10^{-12}$ meters, picometers. In physics, there are two mainframes, the classical frame, which includes Maxwell's electrodynamics, Newton's mechanics, and derivative theories, and the quantum mechanical frame which ...

47

Our eyes have excellent spatial resolution. We can tell the difference between objects only a fraction of a degree apart. This is possible due to both the construction of the eye and the fact that visible light has wavelengths that are tiny on our scale. Signals that arrive simultaneously can be independently detected. Our ears do not have this level of ...

45

No, because of the sizes of their surfaces. Let's make these simplified assumptions: The Earth and the Moon are both spheres 1 AU from the Sun. The total amount of sunlight an object receives is proportional to the solid angle it takes up from the Sun's point of view. The Sun and the Moon are each visible from a hemisphere of the Earth. Then the total ...

42

The reflected light is moving toward/into your eye, while the light just passing by you isn't. You can see light that's not "reflected", like the light emitted by a light bulb, there's nothing special about reflected light. All that's needed to see light is the light actually hitting your retina.

42

Yes, good eye! My suspicion is that the ghost images are from reflections off the glass on your mirror. The entire image is getting ghosted (not just your LED), but the ghosts are weak (~5% of the normal reflection), so you can only see it for the bright green light on the black background. So why is there a ghost to the left and right of the image? ...

42

This is beautifully explained by Feynman using his path integrals. I cannot hope to do it better, but just a quick non-mathematical overview. What is mind-blowing about the theory is that you assume that individual photon (on quantum electrodynamics level) is actually "reflected" in each possible direction by each atom of the mirror surface. If you ...

40

It is the bright light from the bub reflecting off the image sensor in the camera, then reflecting off the back of one of the lenses and then hitting a different bit of the sensor where it is detected. Even if the sensor is absorbing 95% of the light hitting it (ideally you want the sensor to absorb 100%) and the lenses reflect only 5% you still have 5% * ...

40

You seem to be asking if the reflection of the sun from a spherical mirror, a convex surface would be the same as the reflection from a flat mirror. A convex mirror is dispersive The image in the diagram above is a virtual image. Light does not actually pass through the image location. It only appears to observers as though all the reflected light from ...

35

Yes, it would continue. But not forever, for two reasons. One is that no mirror is perfect, so a bit of light is lost at each bounce. The other is that no beam of light is perfectly parallel ("collimated"), so that the light spreads out over time, and light eventually falls outside the mirror. Edits after comments Spherical mirrors will help, but they ...

34

Telescope mirrors and other mirrors used by scientists telescopes regularly do use a silver coating. See for instance here. However, aluminum coating are the norm (certainly for the large primary mirrors deployed in telescopes) because of durability reasons. I quote from the text linked to above: The challenge with using silver as a coating material is ...

33

The important thing to notice here is that the layer of black goes behind the Mylar layer. So the light that will be absorbed is whatever penetrated the surface aluminum layer (a small fraction). That is, most of the light will be reflected off the front surface, and only a small amount will be affected by this choice. Now we ask "Why don't we want that ...

33

Although a single photon can only be absorbed and emitted by a single electron, it leaves that electron in exactly its original state. There is no record, and no way of knowing, which electron absorbed and emitted the photon. According to quantum theory, to calculate the result when any electron could have absorbed and emitted the photon, we must form a ...

32

The highest resolution 3d printers I know of are around 1600dpi, which is a resolution of about 15$\mu m$. Telescope mirrors have to be smooth to fractions of a wavelength of light, so the resolution of current printers is nowhere near good enough. Whether 3D printers could one day be good enough is a different question, but given that the improvement in ...

31

That's a good question. Without realising it you have stumbled across the Huygens-Fresnel principle. The starting point it that a single silver atom is far smaller than the wavelength of light, so any scattering from it will be isotropic i.e. it will scatter the light equally in all directions. But suppose we have two silver atoms side by side. Each atom ...

31

That's precisely why a single sharp image is formed. Extend all three reflected rays back below the surface to see where the light seems to come from. If your drawing is precise enough, you'll find that they intersect at a single point, which is precisely the mirror image of the object. The point of specular reflection is that the light seems to come from ...

29

This is a grossly exaggerated illustration of a strictly cylindrical metal tube compared to a cylindrical tube with external diameter variations, like the one you have in your case: Because of those diameter variations, the reflected light can vary between scattering and concentrating on the surfaces it is reflected onto. bonus reflection gif: http://i....

27

The simple answer is that the two devices work in completely different ways. Solar cookers, as well as so-called 'solar thermal collectors', focus the light of the sun to heat something (a pot in a cooker, some oil or ceramics) and the heat is then transferred somewhere, where it generates electricity, usually by some steam engine. So, the more heat, the ...

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