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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Theoretically, is it necessary that if light passes through a glass slab, its intensity should decrease?

Is it necessary that for an E/M wave of given frequency which can pass through a medium of given refractive index, it should lose some of its intensity. Practically, this must be necessary because of ...
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1answer
51 views

Polarization of light upon reflection

I was wondering (since I've looked pretty hard and haven't been able to find anything)- are there any models that explain the polarization of light upon reflection? Everywhere I've looked I've seen ...
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1answer
65 views

Difference between speed of light and of bullet after passing through a barrier [duplicate]

I just read that, when a ray of light traveling in vacuum at $c$ strikes a glass slab, its speed decreases and then when it re-emerges it gets back to its original speed i.e $c$. If I draw a ...
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1answer
50 views

Sound waves and chromism?

I am definitely not a physicist, but I have a question related to Physics so I thought I'd give it a try. Please excuse my ignorance. :) I am somewhat familiar with the changes in color caused by ...
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2answers
105 views

Why do we see light and isn't everything dark?

Suppose it is dark. If someone shines a flashlight directly at you, you see light. If, however, someone shines a flashlight at something else, you see that thing illuminated, but you don't see the ...
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1answer
54 views

What is the relationship between $a$ and $m$

$a$ is defined in HERE What is the relationship between the length-scale $a$ and the mass $m$?
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0answers
22 views

circular orbits in general relativity [duplicate]

I am studying the derivation of the circular orbits of particles in general relativity (Derivation) Question 1: What is the meaning of the constants $a$ and $b$, it says they are " length-scales", ...
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1answer
32 views

Conservation of Energy in Blue Shift

Imagine light coming down and hitting a neutron star. It light is blue-shifted. I know that energy/mass is conserved and that the energy to blue-shift it comes from the gravitational field, but how is ...
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1answer
186 views

A yellow lemon is illuminated by green light. What color does the lemon appear?

I think it's blue, but I'm not sure. Is there a way to find out without simply testing it?
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1answer
103 views

Find the electric field of light due to an LED [closed]

This is a JEE mains question which neither me, nor any of my teachers can figure out. Help me here. "A red LED emits light at 0.1 watt uniformly around it. The amplitude of the electric field of the ...
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3answers
84 views

UV filter, does it exist?

On the video here https://www.youtube.com/watch?v=o9BqrSAHbTc, Thomas Leveritt uses a UV filter which, as far as I understand, lets only the UV through. I couldn't find any photo filter that do that. ...
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2answers
91 views

What happens when both of Polarizing filter in LCD screen are Horizontal

What would be the result if we replace the vertical polarizing filter in LCD device (screen) with a horizontal filter, what could we see exactly? Would we see the same if we use only one horizontal ...
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1answer
27 views

How to combine contributions of individual type of cone cell sensitivity to get the human luminosity function?

As shown in this figure from some computer vision book: The data of three types of cone spectral responses is pulled down from: http://cvrl.ioo.ucl.ac.uk/cones.htm It is said that the Long, Medium ...
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1answer
60 views

What are the units of color matching functions?

In some computer vision book I read lately, the color matching function is invoked without clear definition of its units. I suspect the color matching functions are spectral irradiance or spectral ...
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1answer
44 views

Interference and windows

The other day i was learning about interference patterns with the effect of a bubble making a rainbow on the surface. I learned that the reflections from both sides of the soap can interfere ...
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2answers
135 views

Special Relativity - Distance Not Increased?

I just watched the movie Interstellar and the question was asked of why/how high-speed travel would slow time within an area. Curious as I am, I watched several YouTube videos to quickly 'educate' ...
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1answer
35 views

Path length requirement for diffraction problem [closed]

The following question has been asked in a problem sheet I have been asked to answer: "The above diagram relates to the path lengths of radiation, with an angle of incidence, θ, reflecting off ...
2
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2answers
48 views

Color of objects in Yellow sun

The sun appears yellow but the objects on the earth appear as if they have been illuminated in white light. Are all objects that we see in sunlight actually in a yellow shade, and would appear ...
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1answer
28 views

Florescents and radio waves

Okay so if you put a florescent light bulb in front of a certain radio, the radio waves excite the mercury inside a causes them to emit UV light which makes the outer coating of the light bulb light ...
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1answer
68 views

Surfaces that reflect UV rays

I've been trying to research what surfaces reflect UV rays for the past day but it's been difficult coming up with definitive answers. So far what I've found is that surfaces that reflect visible ...
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3answers
1k views

Why does red light travel faster than blue light?

I know that light of all frequencies travel at the same speed in vacuum. But I wonder why their speed differ in any other medium, why does red light travel faster if it has less energy than blue ...
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1answer
52 views

Polarization vector identity in Minkowski space?

Playing around with numerical light-like momenta $p^\mu_1,p^\mu_2$ (light-like meaning ${p_1}^\mu {p_1}_\mu={p_2}^\mu {p_2}_\mu=0$) and corresponding polarization vectors ...
4
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1answer
99 views

What causes these rainbow effects using a polarizing filter on an airplane?

I know that light reflected from a surface at 45° is polarized and that for a similar reason skylight arriving from a direction orthogonal to the sun is polarized too. Photographers make use of this ...
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1answer
257 views

Does my green laser pointer emit three distinct frequencies, or is my measurement flawed?

I was playing around with a cheap diffraction grating and my set of laser pointers, and I noticed that while the red and the blue pointers produce a single point in the spectrum, my green laser ...
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1answer
82 views

Laser diode spectrum vs LED spectrum, why so much difference in broadness?

I've been reading about how light is produced in both laser diodes (the most common types of lasers) and LED's. The mechanism seems very similar if not exactly the same: one applies a potential ...
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2answers
108 views

Does a source emitting visible light also emit infrared, microwave and radio waves?

I have a bulb which is hot enough to emit visible light and obviously it's hot enough to emit radiation which lies before the visible light temperature i.e. radio waves, microwaves, and infrared ...
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2answers
99 views

Why does the light instantly disappear when we switch off the source?

For example i take a box which is completely covered by the most perfect mirrors possible inside and inside that box i have a bulb whose bulb holder is also covered with the most perfect mirrors ...
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3answers
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Why doesn't light affect a compass?

In our daily life a lot of photons of visible light, infrared and radio etc move around us. We know that light is an electromagnetic radiation. So why doesn't that electromagnetic radiation affect a ...
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2answers
106 views

Does a photon travel in all directions?

For example i am standing and a beam of light is passing in front of me. I am able to see that beam of light so does it mean that photons are travelling in all directions other than the photons which ...
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2answers
893 views

Why do we use microwaves in microwave oven?

We know that any object above absolute zero emits electromagnetic radiation. So hotter the object shorter the wavelengths. In the electromagnetic radiation spectrum radio waves has the longest then ...
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1answer
77 views

How to build a MOKE (magneto-optic Kerr effect) magnetometer at home?

I'd like to build a magnetometer at home. The type does not matter actually that much but it should be doable at home. The MOKE (magneto-optic Kerr effect) magnetometer at least appears to use ...
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0answers
27 views

How is ink's color produced?

From https://en.wikipedia.org/wiki/Complementary_colors The pairs of complementary colors vary depending upon whether the colors are physical (e.g. from pigments), or from light. These change ...
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1answer
88 views

Refraction of light marching band analogy

When trying to understand the refraction of light when it hits a slower medium, lots of people seem to be enlightened by the 'marching band' or 'marching soldiers' analogy, which 'explains' that when ...
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1answer
50 views

Interference of waves

Every thing has a dual nature. So if we take waves(consider light interference) as particles, exactly what happens during interference (both constructive and destructive)? Can you explain in easy ...
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1answer
97 views

Why “colours” of light are given in wavelength not frequency?

If I understand correctly, when a beam of (monochromatic) light passes through media of different refractive indices, its wavelength changes but frequency remains constant. Why, then, are colours of ...
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0answers
32 views

Why does the spectrum for deuterium show a weak line at H-alpha?

I was wondering why the spectrum for deuterium shows a weak line at H-alpha, the first line in the hydrogen spectrum.
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0answers
41 views

Beating the Diffraction Limit with NSOM

I am trying to understand exactly why we can beat the diffraction limit when using near-field scanning optical microscopy (NSOM). For those who aren't familiar with NSOM, check out this article: ...
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2answers
89 views

Models of light

As far as I'm aware, there are two different (and almost contradictory) models that describe the behavior of light: light as a wave (EM), and light as a particle (QM). From what I've heard, depending ...
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1answer
61 views

What happens if light is trapped between two points?

The image can explain my question In the image light is clearly trapped.Even if the mirror absorbs energy the light is continously being added, will there be enough force to break the mirror?
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2answers
135 views

Why doesn't the Sun appear green to our eyes?

The spectrum of the Sun as seen at sea level can be seen at https://commons.wikimedia.org/wiki/File:Solar_Spectrum.png so we can see that wavelengths around green to yellow are the ones that are the ...
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3answers
220 views

Is purple in visible light?

This isn’t a duplicate. I read those pages, but those didn’t answer my questions. Please watch this. Does visible light consist of red, orange, yellow, green, cyan and blue? No purple? My definition ...
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3answers
201 views

Why most of physics is somehow related to light? [closed]

It seems that for the past 200 years, every physicist is concerned about light. For example : Newton's particle model, Young experiment, Photo-Electrict effect and Einstein's formula, Special ...
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2answers
64 views

Velocity of light

Velocity of light decreases as it enters a more optically denser medium. So how far can the velocity of light be reduced? Which object has the highest refractive index?
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1answer
48 views

Shadow of a ripple?

Suppose a stone is thrown into a pool of crystal clear water and its a bright sunshiny morning. You can observe a shadow of the wave in the bottom of the pool. Why does this happen? Is it due to ...
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1answer
140 views

What causes light to travel through a curved fountain of water?

Today I observed a tilted fountain spurting water upward (the water fell smoothly; no detectable turbulence). A colored light was shown upward into the water as it left its source. This light traveled ...
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1answer
819 views

Test whether a glass prevents you from getting your Vitamin D portion?

I work in an office with glass, which I believe filters the UV radiation of the sunlight. Is it possible to test if exposure to the light coming through the glass will supply Vitamin D for me as a ...
3
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1answer
163 views

Young's double slit experiment and intensity

I want to ask a question about double slit interference and the pattern that it produces on a screen (for example in Young's Experiment with a laser beam). I understand the reason that you see a ...
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2answers
134 views

Why is the spectrum of a blue flame the way it is?

In the spectrum of the blue part in a candle flame, there’s a violet emission at 432 nm due to excited CH* molecules (chemiluminescence). Why 432? Why not 400 or 500? There are emissions at 436, 475 ...
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2answers
97 views

How can shadows ever be sharp?

When I hold my hand underneath my lamp, the shadow my hand casts is crisp and sharp, meaning that the edges are well defined and not blurred. But according to Huygen's principle, shouldn't the light ...
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2answers
91 views

Why is there lightning where there are no clouds?

Recently my family and I went onto the balcony to observed the stars in the night sky. We started to see flashes in the sky and we realized that it was lightning (non fork lightning). I looked around ...