Questions related to the perception and measurement of light (primarily in the visible range), its mathematical description, the reproduction of colors by different means, color combinations, etc. Please use the tag [electromagnetic-radiation] if you want to refer to the general form of light.

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Why are black holes black? [duplicate]

If heard two explanations for this. One explanation is that the gravity is so strong that space is being stretched inward faster than the speed of light and thus no photons could possibly escape. The ...
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2answers
114 views

Why the incessant confusion between diffraction and interference? [closed]

Feynman said, "No one has ever been able to define the difference between interference and diffraction satisfactorily. It is just a question of usage, and there is no specific, important physical ...
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2answers
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Refraction of light rays

My textbook says that the greater the refractive index of a medium, the lower the speed of a light ray passing through it. Seawater has a slightly larger refractive index than fresh water. Light ray ...
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2answers
166 views

Nature of light in Special Relativity

What is the nature of light in the context of Special Relativity? Is it a photon, or an electromagnetic wave, or something else? I have doubts, because a photon seems to me a quantum mechanical ...
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2answers
70 views

Electromagnetic Radiation and Communication!

I read that the accelerated charges create electromagnetic field/spectrum which consists of following different waves: gamma, X-rays, ultraviolet, visible light, infrared, microwaves, & radio ...
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1answer
81 views

Diffraction wavelength relationship [closed]

This question appears somewhat similar to other questions asking about why wavelength affects diffraction (a concept which I'm still not 100% sure on...) however my query is different and not answered ...
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14 views

Is it correct that the polarized scatter of a polarized light source is max. orthogonal to the light source?

First of all, is the statement above correct? And if so, is there a constant gradient, with no polarized scatter parallel to the polarized source up to fully polarized at 90 degrees?
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1answer
46 views

What happens when two polarized lights of the same wavelength interfere at 90 degrees with each other?

am I right in assuming that if I cross two polarized lights of the same wavelength the result would be destructive interference? I don't mean 90 degrees as in 'orthogonal polarization', but the two ...
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6answers
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Light's inverse square law: Does it require a minimum distance from the source?

Does the inverse square law begin to take effect the moment light leaves its source? For example, does light's intensity decrease, i.e. does the area in which the photons might land increase, at a few ...
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31 views

Is it possible to approximately know the wattage/luminosity of a lamp knowing distance and using a DSLR?

I'd like to know if it is possible to approximately know the wattage/luminosity of a lamp knowing distance and using a DSLR (digital single lens reflex camera) mounted on tripod. Maybe, when shooting ...
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Why does some peoples' hair look blue when I look out the train window while wearing sunglasses?

Specifically, when I look through the window, black hair looks blue when people pass the window outside, and black shiny benches look like somebody painted them blue. Pretty sure my sunglasses are ...
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14 views

How does the area of illumination affect the numerical aperture / optical resolution of an optical system?

I have been reading an optics paper in which they designed a microscope with the following setup. A light source passes through a small pinhole, illuminates a sample, which then forms a diffraction ...
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1answer
38 views

What kind of other light sources can disturb the detection of LASER [closed]

My project objective is to detect different lasers , for example Laser Range Finder: pulse width 10ns and repetition rate is ...
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0answers
11 views

When light reflects from a medium of lower index of reflection to a medium of higher index of refraction, why does the light undergo a phase shift? [duplicate]

I learned in my physics class that there is a phase shift when light reflects off a low $n$ from a higher $n$, but never got the explanation.
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3answers
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How is 6W equivalent to 40W, as claimed by adverts for LED light bulbs?

Every advert I come across for LED bulbs advertise them as the equivalent of a higher W incandescent bulbs. This makes no sense to me, if the room requires 40W to lighten it up then it'll always ...
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1answer
30 views

Michleson Interferometer fringe shift

I have a problem with interferometer fringe shift. I am learning it from my physics book. In the book, it is written, "As the L1 (Displacement of moveable mirror) is changed, the pattern of ...
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3answers
657 views

What gives things color? [duplicate]

I know that color comes from things not absorbing a certain wavelength of light, but what property gives something color? Like what property of copper atoms makes copper as a whole brown, or cobalt ...
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1answer
60 views

Why do some elements burn different colors? [duplicate]

I have a torch lighter and it makes a green color when the flame passes over the metal in the center. What on the molecular level would a flame change color although there is no difference in ...
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0answers
20 views

Why emulsions do not show Tyndall Effect?

The particles in an emulsion are large enough than that of solution, but why emulsion does not show Tyndall Effect?
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3answers
103 views

Is this true about low-light/one photon at-a-time double-slit interference?

I've consistently noticed in pictures of double-slit interference when very low-light or one photon at-a-time is used, that there's lots of "stray" photons detected in the areas of destructive ...
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3answers
4k views

Can something without mass exert a force?

I am something of a dilettante in physics, so please forgive me if the answer to this question is painfully obvious. The question is simple, can something that theoretically has no mass exert a force. ...
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1answer
81 views

Backing out of interactions: Does physics account for such a thing?

Does physics account for interactions between light and matter ever being "not completed" or backed out of? Here's what led me to the question. In learning about interference in light, I ended up ...
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1answer
42 views

How does sunlight undergo interference as shown in the video?

As far as I know, for interference to happen in a double-slit experiment, the light source should be coherent and monochromatic. If that is the case then how come sunlight undergo interference and ...
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1answer
31 views

Why is it easier to make inks which show up on white paper than on black? [closed]

Not sure if this is a Physics question, but... Why is it easier for inks to show up on white paper than on black? You can get "special" inks which print solidly on top of black surfaces, but your ...
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1answer
65 views

How does Compton scattering demonstrate particle over wave behavior?

Why is Compton scattering thought to demonstrate light's behavior as a particle over that as a wave. I'm interested in the thoughts at the time of Compton, but also how it contradicts current theory ...
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0answers
23 views

Fresnel Diffraction

In fresenls treatment of a plane wavefront when the aperture is infinty then intensity on the screen must be equal to the intensity of incident wavefront. Intensity comes out to be 1/4 times the ...
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1answer
28 views

Finding Intensity of light incident on a photodiode

Given a halogen lamp(9500lumen,500W) at a distance d from a photodiode. How can I find the intensity of light incident on the photodiode?
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3answers
111 views

Create a laser from sun light

I have read on wikipedia the basic theory behind laser. A photon passes through an excited electron which then produces the exact same photon. Light is bounced off mirrors to create more photons. Is ...
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0answers
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Height of a point in a plane given a measure of luminance

Context Assume a left-hand rule coordinate system and X points right, Y points up, Z points out. I have a camera facing perpendicular to the X-Z plane in the negative Y direction. I have 4 ...
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0answers
20 views

Mirror shake emulation for the light

Is there any way to simulate mirror shaking? Final goal is to make send light beam to the mirror and get reflected beam the same, as it happens if mirror is vibrating. Mechanical vibration is limited ...
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0answers
23 views

Light bulbs Flashing on when disconnected

For the 2nd time I've had a lightbulb flash on in my hand after removing from the power socket. The first time the overhead light in my hallway was out for a couple of days before I got around to ...
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1answer
54 views

Is fire more harmful than a phone?

I have read somewhere that the higher the frequency of electromagnetic radiation, the higher the damage it causes to your body, and visible light has a very high frequency in comparison to microwave ...
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1answer
49 views

What is “Condensed Light”?

It is mentioned in this article It seems to be a Bose-Einstein condensate of some kind, but it is not exactly clear how one can create a BEC with just photons Light consists of tiny indivisible ...
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2answers
57 views

Is the rate of light emissions actually the frequency of the light?

I am confusing with the concept of frequency in the context of Doppler effect studying SR. The Schutz says, if the source emits pulses more frequently, then the observer would see the lights not only ...
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1answer
34 views

Blue light is reflected, red is not. What happens to other visible/non-visible light?

The problem says: The certain film on the glass reflects blue light of wavelength 480nm, but does not reflect any red light of wavelength 640nm. 1) If we say that it reflects blue light but no red ...
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Can 2 photons make up the same colour as another photon?

So, my question deals with the excited electron shown above. (1st diagram) This electron can return to its ground state by either of two ways. One of the ways involves the emission of 2 photons. (2nd ...
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1answer
57 views

Glowing light around my shadow during sunrise

This morning I was jogging when the sun came rose. I was in the middle of wheat-fields and noticed that there was a glow around the upper part of body's shadow on the fields. At first I thought that ...
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1answer
47 views

Explain Sun Glare

Above is a picture that I took just before the sun set. Notice the prominent red blob to the left of the sun. Can anyone explain the phenomenon that creates superimposed shapes and blobs in images of ...
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1answer
54 views

Basic question about light

My understanding is: when light hits an object, it can do one of three things: transmit through the object, be absorbed into the object, or reflect from the object. However, I have also learned that ...
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2answers
265 views

Is light getting another color when travelling through a prism?

When white light travels through a prism the speed of this light is slowed down. Now there is a relation between speed of light, frequency and wavelength. So when a red light of 700nm enters a prism ...
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0answers
18 views

Is there a limit to the frequency of light? [duplicate]

I am assuming that light frequency would eventually be limited by Planck distance and/or Heisenberg limitations. Could this frequency ever be approached in practical terms?
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2answers
274 views

Why is infrared radiation associated with heat?

I am little confused with infrared radiation. I understand that when an object is hotter, it radiates electromagnetic waves of a bigger frequency and this waves are also more energetic, that is why ...
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1answer
44 views

Is it scientifically possible to stop a screens polarization by adding a layer? [closed]

Back story: At work we deal with confidential data, however our desk layout does not allow for screen privacy. We do not a privacy screens and are not allowed to take apart our screens. In searching ...
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1answer
50 views

why my eyesight glasses the color of the things I see?

I have started to need eyesight glasses (I am short-sighted) a while ago and I am puzzled by the fact that when I wear my glasses the color of the things around me are less bright than when I don't ...
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3answers
147 views

Do gravitational waves affect light?

Gravity "bends" light, predicted with theory of relativity and subsequently observed: how does gravity and gravitational waves achieve this effect, and shouldn't this effect be present wherever there'...
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0answers
60 views

Cherenkov Luminescence Imaging, Cherenkov radiation,

Is it possible to see glowing from Thin Layer chromatography (TLC silica gel on Aluminium) when we image it by IVIS spectrum (no radioactive source)?
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1answer
40 views

Sphere, silver reflector, refraction questions

A sphere with its back silvered can act as a retroreflector. When a fine beam of light is directed to the sphere as shown, it is refracted at the front surface, and focused on the rear interior ...
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1answer
37 views

Tricky Optics Questions, shifting lenses [closed]

A candle is placed at a fixed distance in front of a wall. A lens is inserted and moved slowly between them. At two particular positions, sharp images are formed on the wall. The heights of the images ...
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1answer
86 views

Given is an object which is cyan when illuminated with white light. What is the perceived colour of the object when illuminated with yellow light?

I know the perceived colour of an object depends on which wavelengths of the incoming light are reflected and not absorbed, which lead me to believe that it is impossible to be red or yellow... I ...
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Doppler shift of light from stars and galaxies [duplicate]

I was reading about how we can ascertain whether a cosmic object is receding from or approaching us by studying the doppler shift of its spectrum- I mean the redshift and blue-shift. But we have no ...