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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Is light scattering the same as diffuse reflection?

I am doing an assignment on how the eye perceives things for a biology class, and I am confused about the two concepts. I have only seen light scattering ascribed to single particles, as in Rayleigh ...
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5answers
103 views

White, is it a colour or absence of colours?

Our chemistry sir and we had an argument today at the lab, he says that white actually is not a colour, it is the abscence of colour, but we say that it is a colour and we gave the following point to ...
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3answers
44 views

What is meant by phase, phase difference, in(and out of) phase in wave terminology?

What is meant by phase, phase difference, in(and out of) phase in wave terminology? How do you get the relation $y=sin(\omega t + \phi)$. Since the graph of sin function is identical to that of a sin ...
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2answers
100 views

Explain the notion of light/electromagnetic waves/photons to a non-physicist

A non-physicist asked me about special relativity. My explanations naturally were based on gedankenexperiments involving light. This forced the question: "What is light? It is particles, isn't? Or is ...
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3answers
31 views

Frequency dependence of the speed of light in air

According to this link, the speed of light of different colors in a medium should be different. But if the refractive index of light in air is 1 then this means that the speed of light in air and ...
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0answers
30 views

Is this fine to think of light as the following? [on hold]

Is light quantums (increments [photons]) of the electromagnetic waves which are synchronized by oscillations of electromagnetic fields
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1answer
33 views

How many foci does a converging or diverging lens have?

I thought this was a simple question but can't seem to find a direct answer. In ray diagrams with a converging or diverging lens, we always draw F (the focal length) on both sides of the lens. But ...
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1answer
76 views

How do photons carry information?

In cosmology it's frequently said that photons from the early universe carry information from that time. However, wouldn't they also carry data from later interactions? How do we differentiate ...
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0answers
42 views

Interstellar Movie: Black hole shown in the movie [duplicate]

In the interstellar movie, the black hole shown has a ring of light orbiting around it. From what I know, (correct me if I'm wrong) that light is unable to escape the gravity of the blackhole and ...
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2answers
57 views

Understanding colored shadows [on hold]

When I turn on white lights, these chairs cast a shadow. However, when blue LED lights are turned on the shadow turns yellow. Why is this? Is this due to interference of light or is it just an ...
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1answer
71 views

Basic rule for diffraction

I'm a high school student. I still don't understand the reflection, diffraction and refraction of light. It seems to me that in concept of quantum physics, reflection is just a process of object ...
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1answer
43 views

How much lux does the sun emit?

I want to know how much lux the sun emits on a bright day - I don't mean when one stares directly at the sun, but rather when one walks casually outside when the sun is shinning brightly. Now the ...
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1answer
19 views

What material would block (reflect, appear opaque) IR light 750-850nm range, but allow visible light to pass? [on hold]

I'd like to find a material, ideally a plastic, that would prevent IR light from passing , but appear as transparent as possible to visible light. I've sampled some plascolite products and they work, ...
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2answers
93 views

Why does a circle of light appear when I shine a laser pointer at a wire? [duplicate]

When I point a laser at a wire , a circle of light appears on a wall behind it . why this happens. What is the circle of light and why does it appear? Could anyone give some tips on what I should ...
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1answer
71 views

Dispersion in a rectangular prism

Why are the colours visible only at the fringes of the light refracted through a rectangular prism?
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2answers
55 views

Why are solar panels blue, rather than black, when black absorbs more light?

This is an image of a solar panel array, courtesy of Wikipedia. Some of these look rather black, but most of them are blue. As far as I know, solar panels work by absorbing "light energy", and ...
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1answer
18 views

How does the flow of photons (qty/s) vary across the spectrum? (In everyday life)

Humans see only a narrow band of light wavelengths. Many animals see much deeper into infrared. Maybe one clue to explain why we don't see IR naturally, has to do with the light intensity as a ...
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1answer
2k views

Refractive Index formula for denser to rarer medium

I learnt that the formula for refractive index when light travels from rarer to denser medium is $$\frac{\sin i }{ \sin r}$$ where $i =$ angle of incidence, $r =$ angle of refraction. Is the same ...
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1answer
280 views

Radiant intensity in terms of angle with the surface

This problem is about color science and it is short but tricky: where do you get $I_p=\frac{P}{4 \pi r^2} \sin \alpha$, where $I_p$ is radiant intensity and $\alpha$ is the angle between the ray and ...
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2answers
31 views

What should be the width of the slit in single slit diffraction experiment?

What should be the width of the slit in single slit diffraction experiment? If the wavelength is taken lambda while doing experiment.
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3answers
10k views

What exactly is a quantum of light?

I am currently trying to learn some basic quantum mechanics and I am a bit confused. Wikipedia defines a photon as a quantum of light, which it further explains as some kind of a wave-packet. What ...
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0answers
28 views

How is the formation of the first atoms related to the cosmic microwave background? [duplicate]

Common atoms formed when the universe finally got cool enough for electrons to bind with atomic nuclei around the year 380,000. From what I understand this shift in state from plasma to discrete atoms ...
2
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1answer
156 views

Why does light not slow down?

Clearly light bounces off of things, going really really fast. I'm curious to understand how light interacts with matter in order to bounce without: Applying force to the object Losing speed So my ...
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0answers
16 views

Making sense of sinogram of perspex block in air

I'm confused trying to visualize what happened exactly during this experiment: Setup with a laser and a photo diode on the opposite side. A perspex block (2x2cm) in between. Take 200 measurements ...
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3answers
111 views

How are photons made?

I mean in manufacturing a bicycle we know how to "ensemble" a bicycle, what actions and "assembly of parts". So what steps are needed for make a photon? Also is there a limit on how many photons for ...
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0answers
33 views

Reflection and refraction of light [duplicate]

When a light ray strikes an interface a part of it gets reflected, a part of it gets absorbed while another part gets refracted. Why does light reflect? Why does it refract?
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0answers
16 views

Idea About Combining the Light Models [closed]

This is probably going to sound very silly, but I learned that light has three different models: particle, wave and ray. So why can't it be that light is really a stream of particles that are moving ...
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0answers
46 views

How can spacetime affect massless entities? [duplicate]

Why is light affected and "bent" by spacetime if it has no mass or density?
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2answers
77 views

Why does light travel as waves? [duplicate]

Why does light travel as waves instead of say just a straight line? What are the forces that make a light photon travel in a wavelike pattern?
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1answer
33 views

Why would a sweeping LIDAR or RADAR beam not produce an artificial Doppler shift?

Assuming a bi-static Radar or LIDAR with a stationary transmitter and a stationary target and a stationary receiver, with a sweeping RADAR/LIDAR beam reflecting off a stationary target: Why would the ...
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2answers
77 views

Light wave crossing media and the relationship between speed, wavelength, and frequency

There are many threads on this topic (like this one) but one aspect about the equation $ v = \lambda\nu $ still confuses me. I have read that frequency does not change when light crosses into ...
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2answers
48 views

Why does the thought experiment of a photon bouncing of a mirror imply anything for other objects?

Okay, so I am reading a book, "The Elegant Universe" by Brian Greene, which talks about motion and its effect on time. Greene makes the point that time changes with motion by saying that if you have ...
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0answers
15 views

Can a patterned microwave beam with alternating frequencies be created?

Is there a way to create a patterned microwave beam with alternating frequencies such that, in the far field, from top to bottom of beam, there is repeated pattern of Wavelength one, Wavelength two, ...
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4answers
4k 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 ...
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2answers
150 views

Light-matter interaction and an object's appearance

I am taking a course in Computer Graphics, and the teacher said we could put materials in there main categories: mirror like glossy or specular diffuse He suggested that the law of reflection is ...
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3answers
830 views

Can a glass window protect from heat radiation?

I have been reading in this and found a statement saying : " Glass will not transmit heat radiation.". So now I am confused. If glass won't transmit heat radiation, then why do we feel hot when we sit ...
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1answer
49 views

Gravitational lensing not caused by gravity?

This may be a possible duplicate, though I recently stumbled upon this paper http://arxiv.org/abs/1004.1467 claiming to have an alternative explanation of the interaction of light around massive ...
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0answers
18 views

What sort of function would accurately model the change in daylight at sunrise or sunset?

Assume that you are standing on the equator in a flat, wide-open space and there is no moon or clouds. What sort of mathematical function would accurately model the increase in daylight when night ...
4
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1answer
47 views

How can absorption spectra form if atoms can't remain in an excited state?

I have been tasked to write a research paper on stars. However, I know very little about physics in general. I am learning about how we can glean information about stars by analyzing the light that ...
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1answer
75 views

relation between photon number and energy

Suppose there are two light beams. One is red while the other is violet. The energy of both is the same. Which one of these beams has a larger number of photons, or is the number of photons relevant? ...
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4answers
30k views

What do ants see?

After watching some ants in my garden today, and then looking at this very illuminating demonstration, I got to wondering, about what they would see. Not specifically ants (I understand their ...
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6answers
2k views

Why is air invisible?

I think that something is invisible if it's isolated particles are smaller than the wavelength of visible light. Is this correct? Why is air invisible? What about other gases and fumes which are ...
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0answers
21 views

Why are trampolines more likely to give you a static shock when it is sunny?

It could just be in my head but I have noticed that I am more likely to get a static shock from my tramp when it is sunny than when it is not sunny. Is there a reason for this?
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1answer
162 views

What the name of the evacuated glass gadget with black and white vanes that turn when a light is applied?

I remember a glass device my physics teacher had at high school which Contained some vanes mounted somehow on a vertical axis, which were all black on one side and white on the other Was in a ...
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2answers
35 views

Number of different wavelengths in the visible spectrum reaching Earth

I recognize the visible wavelengths of light extend from approximately 400 - 700 nm. But how many different wavelengths exist in that range? 300 ? 30,000 ? (400.01 - 699.99) If it's completely ...
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1answer
43 views

Relation between number of photons and energy?

Please can anyone explain it. If number of photons are increased will it increase the providing energy. Suppose, we are sending a limited number of photons each carrying energy. We have a energy ...
48
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6answers
8k views

Why are most metals gray/silver?

Why do most metals (iron, tin, aluminum, lead, zinc, tungsten, nickel, etc.) appear silver or gray in color? (What atomic characteristics determine the color?) What makes copper and gold have ...
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1answer
164 views

Scanning electron microscope imaging

In a scanning electron microscopy, secondary electrons are defined as the electrons which obey inelastic scattering whereas backscattering electron follow elastic scattering. Now my question ...
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1answer
25 views

Does the color of refractive medium affects the color of refracted light?

Imagine if I have a red colored prism that splits white light ray into its seven components, would the red component be affected by the red color of the glass material of the prism in any which way? I ...
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2answers
68 views

Attributes of polarized light [on hold]

Which of the following is true for a polarized light? The electric vector is constant in its module and direction The electric vector oscillates in every plane that passes through the ...