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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3
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2answers
129 views

What is the energy distribution of light if it has an infinite length?

What is the energy distribution of light if it has an infinite length? I have read in one of the answers here on phys.SE that light has actually an infinite length. But then what is the energy ...
2
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2answers
114 views

Can we have light through out the house with out light being switched on for all the time?

Optical fibres are used to transmit light from one place to the other along curved path in a more effective manner. The optical fibres consist of thousands of strands of a very fine quality glass or ...
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5answers
88 views

If you shoot a light beam behind the event horizon of a black hole, what happens to the light?

I have a couple of questions about light here, and sorry of they are silly.. So since anything that goes beyond the event horizon can't go out, so what if a light beam was pointed somewhere behind ...
16
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4answers
2k views

When photons reach us, what exactly is happening to us and to that photon?

I'm new to physics and am just going through some of the free online classes at World Science U, and after watching this video on the nature of the speed of light and its constancy, a question came to ...
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2answers
48 views

Does any substance possess the property color? [on hold]

A substance possess color according to the color which it reflects. Such as a leaf is green in color because it reflects green. When there is no light, leaf may appear black in color. So is there a ...
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0answers
39 views

What is the age of the Universe from the big-bang light perspective?

What is the age of the Universe from the big-bang light perspective? We all agree that the universe is around 14 billion years, from the perspective of a hypothetical observer moving in a galaxy, ...
3
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3answers
140 views

Will the current carrying solid conductors emit light?

If we pass current through a gas, like in the discharge tube, the electrons will accelerate in the electric field. The accelerated electrons will collide with gas molecules, and transfer some of their ...
0
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1answer
21 views

Why the crest of water absorb more light than the trough of water?

I have done my experiment using water ripple to study the behavior of waves. I know that the crest will absorb more light than the trough so that the image created on the white paper sheet appeared to ...
3
votes
2answers
62 views

Squinting at light sources

I am sure it's just your eyelashes creating a filtering effects, but if you look a a bright(ish) light source such as a lightbulb while squinting, if looks like you are seeing straight light rays ...
0
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0answers
23 views

How do RGB colors work? [duplicate]

They say that all colors can be formed by mixing Red, Green, and Blue appropriately. Is it true? Isn't the Fourier basis infinite dimensional? Or does it turn out to be the case that only three ...
1
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4answers
81 views

Can't virtual images be put on a screen?

Apparently the plane mirror makes virtual images, and virtual images cannot be projected onto a screen. If you look below, it is? If the eye is basically a screen of rods and cones, then everything ...
1
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1answer
33 views

Does a high energy photon experience deceleration or direction-change when it impinge into water or something due to the change of refraction index?

Wave experiences refraction when it propagates into another medium which has different refraction index. Lights surely does experience refraction at the border of mediums which have different ...
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3answers
50 views

Do atoms of a surface excite to reflect the light?

How do surfaces reflect certain colours and absorb the others?
5
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2answers
183 views

Which solution to the electromagnetic wave equation is the most accurate model of monochromatic light?

When a photon is modeled as a monochromatic electromagnetic wave its electric and magnetic components are usually taken to be sine waves (for example here ...
0
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1answer
26 views

Calculating the distance between Detector and Double Slit

I have a little problem that is kind of confusing me at the moment. The following task: Light of the wavelength $\lambda = 500nm$ hits a double slit whose distance is $a = 30\mu m$. Each is $a = ...
2
votes
3answers
64 views

Why can colors be mixed? [duplicate]

We can combine colored light, creating other colors, at least in terms of visual perception. But how it the result physically "a different color" - if it is at all? Or is all this not a physical ...
2
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0answers
150 views

Would there be emf induced in our body due to electromagnetic radiations?

The experiments of innovative Faraday and Joseph Henry in USA, conducted around 1830, demonstrated conclusively that electric currents were induced in closed coils when subjected to changing magnetic ...
0
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2answers
46 views

How camera flash can send information

Nikon have CLS a system that allow to trigger one flash with other flash. I don't know how exactly it work from user point of view, I think that one flash (in command mode) can send information like ...
4
votes
2answers
907 views

Why doesn't my pinhole camera work?

We all know that light travels in straight a line, which can be proved by pinhole imaging as in the picture shown : But when I'm doing this little experiment with an apple, no matter how I change ...
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1answer
58 views

How car headlight works?

There are two headlight of car. One having a light bulb between two concave mirrors (one mirror behind and other infront of bulb), and the other type of light only have one concave mirror behind the ...
4
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3answers
599 views

Why do electrons around nucleus radiate light according to classical physics

As I navigate through physics stackexchange, I noticed Electron model under Maxwell's theory. Electrons radiate light when revolving around nucleus? Why is it so obvious? Note that I do not know ...
-2
votes
1answer
44 views

About light waves [closed]

I read about the Michelson-Morley experiment (forgive spelling) showing Ether as an unnecessary concept for what might have been a medium for light waves. What if space-time is 'saturated' with so ...
19
votes
4answers
1k views

What is the mechanism behind the slowdown of light/photons in a transparent medium?

So light travels slower in glass (for example) than in a vacuum. What causes light to slow down? Or: How does it slow down? If light passes through the medium, is it not essentially traveling in the ...
0
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1answer
32 views

Visual Fields testing: Decibels of sensitivity - meaning

Automated Visual Field test measures the patient light sensitivity in decibels. Questions: If one point has sensitivity of 30 decibels and another point has sensitivity of 27 decibels does it mean ...
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votes
2answers
1k views

Real and imaginary parts of dielectric constant vs refractive index?

So for a complex dielectric constant $\epsilon = \epsilon_a + i\epsilon_b$, the wave vector and index of refraction are related to it through $k = \frac{\omega}{c}n$ and $n = \sqrt{\frac{\mu ...
2
votes
2answers
217 views

Finding the illuminance from a triangular light source

Since most light sources in games are point-like, it's pretty difficult to approximate area light sources with point sources. As triangles are a universal form to represent 3D models (thus area light ...
1
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1answer
37 views

How do projectors work?

So, objects are certain colors because they are absorbing every color except for that one. So why is it that if I take a projector and project a blue image on a red wall, the red wall still reflects ...
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6answers
5k views

Why can't light escape from a classical black hole?

Photons do not have (rest) mass (that's why they can move at speed of "light"). So, my question is how the gravity of classical$^1$ black hole can stop light from escaping? -- $^1$ We ignore ...
1
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1answer
21 views

galaxies fading away after time [duplicate]

Dark energy is constantly pulling all objects away from each other with increasing speed. This in turn causes a red-shift of the light from the most distant object where this effect is most profound. ...
0
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2answers
290 views

Reflections in Rearview Mirror

Why is it that in the reflection in the rear view mirror of your vehicle in the car behind you The driver is on the drivers side and the passenger is on the passenger side and when they raise thier ...
0
votes
1answer
19 views

Why do the RGB gamut vertexes not intersect the edges of human vision on the CIExy plot?

As I understand, the CIExy graphic maps "greenness", or rather middle-wavelengthness, to the Y axis and "redness", or rather long-wavelengtsness, to the X axis. The trapping used to reduce the 3d ...
0
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0answers
38 views

Light emanating from finger tips?

My little nephew on two occasions (when he was 4 now 6) said he saw light rays emanating from his fingers. His father said this is true and that there is physics behind it. I have searched the ...
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2answers
68 views

Why doesn't the magnetic field polarize when polarizing light?

If the magnetic field doesn't polarize does it follow the electric field path of propagation? or does it vanish?
0
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0answers
20 views

What's the proof that the polarization occur s to the electric field of the light? [duplicate]

What's the proof of the light polarization that it happens to the electric field and not the magnetic field? How did Malus discover that the light is polarized although he didn't see the waves ...
6
votes
7answers
273 views

Is the sun's solar radiance spectrum matching up with water's absorption spectrum just coincidence?

People frequently point out that water has a pretty narrow range in which it isn't very absorbing of light, reaching a minimum at a wavelength of about 500nm: And that our eyes have made good use ...
0
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0answers
77 views

Photons and Black holes

How many photons in one Planck volume would it take to form a tiny black hole? A photon doesn't have mass but it does have energy, $1.0101 \times 10^{-37}$ Joule for red $650$ nm wavelength light if ...
15
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2answers
2k views

Is the “How to break the speed of light” minute physics video wrong?

I am referring to this video, on YouTube, by minutephysics, which has quite a lot of views. In the video it states that if you flick your wrist while pointing a laser that reaches the moon, that the ...
5
votes
2answers
146 views

Why must an integrating sphere be a sphere?

Why must an integrating sphere be a sphere? Why can't it be an integrating cube? What is the difference? Could I use a cube to measure total illuminance like an integrating sphere does?
0
votes
1answer
77 views

photon polarization, uncertainty in Energy

A beam of red light is sent along the $z$ axis through a polaroid filter that passes only $x$ polarized light. The beam is initially polarized at $30$°, and the total energy is $10$ Joules. Estimate ...
5
votes
4answers
111 views

Question about the wave nature of light

I quote from my textbook, " Consider two vertical slits S1 and S2 placed parallel to each other, and a string is passed through them. The end B is fixed and A is given jerks perpendicular to its ...
2
votes
1answer
66 views

What is the intensity of this light?

I am struggling with a derivation that calculates the cross sections for Mie scattering and since the incident light is considered to be a x-polarized plane wave I thought that we would have $$I_i = ...
0
votes
2answers
57 views

What is the transmittance function of a photo filter?

The effect of some photo filters can be summarized in transmission curves such as this one: I do not understand which physical value is modified by the value labeled as "Diffuse Density" in the ...
0
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3answers
777 views

EM waves: How do they travel for billions of km without damping

If a star is 1 billion light years away, it means that the light we see from the star is emmitted billions of years ago. How does this light not undergo a frequency change or get damped inspite of ...
1
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1answer
34 views

Light and Prisms

If you matched the yellow light of one prism to that of the green light of another prism, say through a thin glass pane, what would be the resulting color?
2
votes
2answers
45 views

How is the image in a mirror created without a lens or pinhole?

How is the image in a mirror created without a lens or pinhole? From every point in the world there are infinitely many rays going out. How come the image on a mirror is ok, when there is no pinhole ...
2
votes
2answers
106 views

What will be the relative speed of a photon in a light ray to another photon of opposite direction light ray?

If two light rays start simultaneously in the space from exactly opposite ends in opposite direction that is separated by a distance of 600000 km in a way they meet at the mid point (300000 km from ...
0
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2answers
32 views

How is the image in a mirror created? Are there infinitely many light rays?

How is the image in a mirror created? Are there infinitely many light rays? My motivation for the question is from image processing. We work with images as discrete 2D functions, as matrices. Spatial ...
3
votes
1answer
25 views

How is barometric light porduced?

A shaken sealed glass tube containing liquid mercury in a dark room will glow. This has been know since the 17th century and is called barometric light. How does the addition of potassium ...
39
votes
4answers
3k views

Why is water clear?

Water appears transparent to visible light, yet most other objects are opaque. Why is that? Is there an explanation why water appears transparent? Is water transparent at all wavelengths, or are ...
167
votes
17answers
53k views

A mirror flips left and right, but not up and down

Why is it that when you look in the mirror left and right directions appear flipped, but not the up and down?