# Tag Info

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First of all, the hint is in the words "compressed scale" i.e $L>>d$ . So the lines intersect at a point. They subtend certain angles with the horizontal. When $L$ and $d$ are comparable, the picture is like below: As for your second question, $$l_2 - l_1 = d \tan \theta \,\ (\text{from diagram})$$ $$=d \sin \theta \,\ (\text{since \theta is ... 6 The two beams l_1 and l_2 are not parallel. The angles they make with the horizontal is:$$\theta_{l_1} = \arctan\left(\frac{s-d/2}{L}\right) \theta_{l_2} = \arctan\left(\frac{s+d/2}{L}\right) $$However the difference between these two angles is so small compared with \theta that it is an excellent approximation to assume they are parallel. If ... 1 Regarding the transparency of clouds, I think the size of water drops and ice crystals forming the clouds matters a lot. Larger size of those microparticles will tend to make the cloud's boundary well defined and looks bright white. Opposite, the cloud will look transparent and grey. Light can be reflected and scattered so many ways from and in a cloud that ... 3 The reason is that the index of refraction changes with the temperature. Due to the very hot asphalt, there is a strong temperature gradient in the air. This gradient leads to an changing index of refraction with the distance to the road. This is what you see. 6 The most fundamental answer is that water reflects light because the wave impedance of water is different than the one of air and the electric and magnetic field must be continuous everywhere in space. The important thing to note is that the wave impedance is the fixed ratio of the electric and magnetic field amplitude of the light wave and that the ... 2 Whether a material is reflective or not, and to what extent, is dependent upon the atomic structure of the material. When photons hit a surface, they interact with the atoms of that surface, usually raising the energy level of the electrons. When the electrons re-radiate the energy, the structure of the material determines whether it is released as heat in ... 2 Try fluorescent dye (non-toxic, please!). Highlighter ink can work for ordinary tap water (more detail here). Fluorescent paints and glowsticks can also produce decent amounts of light; however, all three of the above methods do not produce substances that are safe to drink. Always be careful when using dyes and other chemicals in beverages. Putting rum on ... 4 Tonic water fluoresces - if you shine UV (black light) on it, it will glow. From the above link: As a follow-up I did the experiment in my own kitchen - with sparkling water and tonic in two glasses side by side. The same glasses under UV light: To remove any doubt - the glass on the right had the tonic water. I removed the white paper background in ... 1 No, there is nothing that is "keeping light from going faster". The local velocity of light in vacuum can not be different than the standard c=3 \times 10^8{ m\over{sec}}. There are two parts to my answer. 1) When light passes near you in vacuum, you will always measure the standard c=3 \times 10^8{ m\over{sec}} using your local meter stick and ... 3 I wonder why light does not have infinite speed. It does not have infinite speed because the experiment of Michelson and Morley has proven that it has the same constant speed in any reference frame. Moreover, any experiment on electromagnetic waves shows the presence of retarded potentials, that is, events need a certain time to propagate in space once ... 0 If the speed of light were infinite then the laws of physics would be non-local. The way things work in our universe is that the state of a system in the future only depends on the present state of itself an its local neighborhood. E.g., the future state of the Earth one year ahead depends only on the present state inside a bubble of one light year ... 2 The speed of light is determined (in terms of other fundamental constants) by Maxwell's equations. In particular, the speed of light c must satisfy c^2=1/(\mu_0\epsilon_0), where \mu_0 and \epsilon_0 are the permeability and permittivity of the vacuum. Because neither \mu_0 nor \epsilon_0 is equal to zero, the speed of light cannot be infinite, ... 1 To see complete wall (of height l) behind himself, a person requires a plane mirror of at least \frac{1}{3} of the height of wall. It should be noted, as mentioned in the problem, that person is standing in the middle of the room. The ray diagram is more or less like this. The next diagram is however not that good . But for explanation consider it to ... -1 The answer is  \dfrac{L}{2} , where L is the length and height of the wall. When you are standing in such a way that your eyes are at height h, the height of the wall above you is L-h. Now to see that part, you need a mirror of height \dfrac{L-h}{2}  because of  \textit{i=r}, you will be able to see rest \dfrac{L-h}{2} . By the same logic, the ... 4 The number of photons may indeed be finite because the energy of the photon in {\rm J} is$$ E = hf$$where h=6.626\times 10^{-34}{\rm J}\cdot {\rm s} is Planck's constant and f is the frequency in {\rm Hz}. For monochromatic light, the number of photons may be determined from the energy in this simple way because f is a fixed constant:$$ N_{\rm ...

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Light always particle in vacuum because it has no medium That's wrong I'm afraid. If you take a look at LIGO you can read them talking about "ripples in space-time (the fabled “fabric” of the Universe)". These gravitational waves are not particles. Instead, space waves. Because the vacuum is a medium. And whilst electromagnetic light waves aren't the ...

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Infrared radiation is absorbed by water, both atmospheric water vapor and liquid water. Below is a graph of water transmission at various wavelengths. Notice that some rather large bands are completely missing. This light can't reach your eyes because the air absorbs it. Also, our eyeballs are filled with water. This water also absorbs infrared radiation ...

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A nephew-friendly, physics-based explanation: Our brains and nerves work based on electrical impulses, which are little bursts of electrical current. Electricity is what happens when you remove the electrons from one atom or molecule and move them to another one nearby. In some materials, like metals or heavily ionized liquids like blood, it's easy to ...

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Light is made up of photons that are really neither waves nor particles. Sometimes they appear to behave as particles (see photo-electric effect), sometimes as waves (see e.g. diffraction). You have either remembered poorly or your teacher has taught you badly: electromagnetic radiation (photons) doesn't require a medium and does not behave as a particle ...

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Hot objects, such as humans and warm-blooded animals, emit IR-radiation. Few creatures have IR-vision, such as snakes. Significantly, snakes are cold-blooded. IR-vision would be advantageous in a struggle to survive for most creatures; with IR-vision, you could distinguish (hot) living creatures with camouflage from their backgrounds and see (hot) living ...

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I am just rewriting what I wrote in a comment to make it more visible, since I think I found out the answer: the solar spectrum as seen on Earth's surface has much less violet and blue than both green and red according to the first link I posted. So mixing all colors should be slightly like mixing mostly green and red (and yellow/orange) than mixing ...

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Look at the Plank Spectrum for a blackbody with a temperature of our Sun (roughly 6000 Kelvin). Here is a link to one. http://www.physics.usyd.edu.au/~sflammia/Courses/StatMech2014/advanced/2/blackbody.jpg From my understanding, the reason we cannot see outside the visible range is that our eyes evolved to match the spectrum of our sun. So for example with ...

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The human eye is indeed not able to sense such light(*). The retina, which basically covers more than half of the internal wall of the eye has 3 different types of cones (which are photoreceptors, i.e. cells that will transmit an electric signal to the optic nerve if they are excited by light they can sense) that are only sensitive to visible light. The ...

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I don't get this. Surely if the sky is blue in the daytime because the blue light is preferentially scattered, colouring the whole sky blue, like white light in fog, this effect would be even more pronounced at sunset, when there is more atmosphere for the light to pass through and therefore more particles to concentrate the blue light.

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First, The relative permittivity is dimensionless - not units of F/m. It is defined as the ratio of the permeability of the material to that of the vacuum. Second, by selecting a value of 4.7. you are defining the index of refraction to be $\sqrt{4.7}\approx{2.2}$. This is because for a dielectric such as glass, $\mu\approx\mu_0$ so ...

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Might not be the cheapest option, but this has the functionality you need. First a get a silicon photodiode, http://www.osioptoelectronics.com/standard-products/silicon-photodiodes.aspx Then get a blue light pass filter, http://opticalfiltershop.com/product-category/edge-filter/short-wave-pass-filters/ Now you make a circuit with a 1k resistor and connect ...

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The photon is an elementary point "particle". particle between quotation marks because it is not a classical point particle , it is a quantum mechanical entity. Quantum mechanical entities depending on the boundary conditions display sometime classical point-like elementary particle behavior and sometimes have a probability density for their location ...

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Photons are emitted and absorbed. Between emission and absorption there is no proper time because the spacetime interval of lightlike movements is zero. Light is generated by the absorption process, not by the travel of light. So there is no reason to fear that it should be dark.

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You've mixed up which time dilates for which observer, and written yourself into a paradoxical corner: if going closer to the speed of light slows time for the object going that speed, and if time slowing down means going slower, then the conclusion is that "the faster you go, the slower you go." Which obviously doesn't make sense as you've pointed out. ...

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If a photon carried a wristwatch, it would not tick. But us subluminals still see the photon move because for us, time has not stopped.

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Time being a measurable quantity according to the beat of cesium atomic clock, it cannot be stopped. If the light ray hitting your eye is taken as a measure of time. Then you can absolutely stop the time by travelling at the speed of light.

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Broadband Emission from 400 to 2200 nm"...which means it will transmit all mixed wavelength of infrared light between 400 to 2200? Yes, this is correct. But the light intensity will likely not be equal at all wavelengths, but will have some dependence, which may be in your spec sheet. Note that 400 - 700 nm is the visible range. I don't know that ...

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The speed of light is the speed in which all electromagnetic waves travel, not only those in the visible light region of the frequency spectrum. Therefore, the speed of light in a material is an important characteristic for problems related to electromagnetism, regardless of your frequency range.

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The relative permittivity of Teflon is actually $\epsilon_r \approx 2.1$. The velocity of propagation at microwave & RF frequencies is going to be $v_p = \frac{c}{\sqrt\epsilon_r}$ or in terms of the index of refraction we have $v_p = \frac{c}{n}$ which is frequency dependent, and therefore $n_g$ which is the group velocity $n_g = n - ... 0 Within the terms you're using, the beam splitter will appear to randomly send a single photon in one direction or another. Over the long run, a 50% beam splitter will send half the photons in each path. The individual photons will be unchanged in energy/frequency/wavelength, so far as the term "unchanged" is meaningful in this situation. After all, if you ... -2 To answer the question = 'neither' .. any (each) detector (after the half silvered mirror) will only ever 'see' either a single 'complete' photon or none .. One way to 'imagine' this, is to think of a travelling 'probability packet' .. the half silvered mirror splits a single photon (single 'packet') into a pair of entangled 'halves', each half containing ... 2 Fast things appear blurry to your eyes, and the distance from a point on the paper to your pencil is fixed. The distance from an ink dot on the paper, to the tip of your pencil where you press down, cannot change. Call this distance$d\$. The only positions the point is allowed to be at when you spin the page around, are positions that satisfy the equation ...

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Another, unrelated way this can happen is, if you wear thick eyeglasses, they may exhibit chromatic aberration, which you will perceive as rainbow fringes at the edges of objects, especially light sources and dark objects against bright backgrounds. The effect is most obvious if you look at the edge of a light source through the outermost (thickest) part of ...

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To make you simply understand the diamonds are cut in specific shape allowing light to come out of its edge only. The light can enter but due to its refractive index the light is bent and can come out of its edge only so we see it sparkling.Also, refractive index = angle of sine of incident ray / angle of sine of refracted ray Also the mirage are similar ...

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To add to the other answers: without detailed analysis of the light passing through fog, one cannot infer that, just because fog dims the Sun to a level that makes staring at it comfortable, therefore it is safe. The "brightness" of the Sun, and the discomfort that staring at it induces, is only very weakly related to the damage it can do. Indeed, a healthy ...

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I think that from a medical perspective your advice was correct, but your physical explanation of why was not. The wavelength dependence of the extinction due to fog depends on the distribution of particle sizes. If the particles are bigger than the wavelength of light, then the (Mie) scattering and extinction become independent of wavelength, and this I ...

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The damage to the eye from looking at the Sun is thought to be due to high intensity light creating free radicals that attack the cells in the retina. Contrary to popular belief it isn't a simple burning process. To a first process fog attenuates all (visible) wavelengths equally, which is why it's white. If it preferentially absorbed some wavelengths it ...

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There are most likely three LEDs with different colors in that device which are driven by current pulses of different length and timing to achieve an arbitrary RGB color with the least amount of hardware. The result is that you are seeing a stroboscopic effect when you move your eyes fast enough to resolve the timing of the three colors. This is also known ...

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If you coat a blue LED with a phosphor material, some of the blue light will be changed to red, green and yellow light, (which is intended to be seen as white light) and maybe, and I don't know how this could happen, I admit, shaking your head might allow you to resolve these components. I originally had a biology element to this answer, but ...

2

You'd explain it the same way you'd explain it to a fifty year old person. What about this... "As you know, there are different colours ... red, green and so on. The air likes to bounce around these colours. Amazingly enough, the air most likes to bounce around blue. The other colours don't get bounced around as much ... they just go away. So when you ...

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I would keep any explanation to a three year old in wholly immediate, phenomenological terms; let him do the following experiment. As you know, the blueness of the sky's orb is a mostly scattering rather than transmission phenomenon, but this is probably too much detail. I think you need to keep the explanation along the lines of "stuff changes the light ...

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According to http://www.scienceinschool.org/2014/issue28/planck, All you need to calculate Planck's constant is Four LEDs emitting coloured light – one each of red, orange, green and blue. Choose LEDs w Four LEDs emitting coloured light – one each of red, orange, green and blue. Choose LEDs with a clear, colourless casing surrounding the LED, so that ...

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None better than a local university can answer this question with their statement: A clear cloudless day-time sky is blue because molecules in the air scatter blue light from the sun more than they scatter red light. When we look towards the sun at sunset, we see red and orange colours because the blue light has been scattered out and away from the line ...

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