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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217 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 ...
0
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1answer
22 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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2answers
38 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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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 ...
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0answers
17 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
125 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
42 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
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
104 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
54 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
58 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 ...
0
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0answers
19 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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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
58 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 ...
2
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1answer
175 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
28 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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2answers
45 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
70 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 ...
0
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1answer
34 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 ...
0
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3answers
77 views

Does light itself experience time dilation?

This seems weird for me. Every time I see light, I will think, "Hey, that light travels from the past far away from us!" Correct me if there is misconception.
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3answers
110 views

How is it possible for the wavelength of light to change in a medium?

So my physics class has just finished a long unit on optics while at the same time I've been trying to teach myself relativity. I admit my understanding is probably rudimentary, but I figured all the ...
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2answers
63 views

When we light the lamp of a room .Where does the darkness go? [closed]

I asked my father . He replied : Under the sofa -.-
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1answer
76 views

What is the speed of a Photon? [duplicate]

How fast does a Photon travel through space? And is gravity able to influence a Photon's path?
2
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0answers
22 views

Is there a wavelength of electromagnetic radiation that can penetrate iron but reflect off iron oxides?

We can see corrosion or rust because visible light travels through air reflects off the material back through the air and into our eyes. But I am wondering if you could see the corrosion through on ...
2
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1answer
58 views

Propulsion force on a laser pointer?

How to calculate propulsion force on a laser pointer in reaction to the emitted light power in watts? Should I just divide power by speed of light? Since power is energy per unit of time, hence ...
0
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2answers
27 views

Laser beam sensed by scattering

Can a laser beam, whether it is a IR laser or of the visible to human eye spectrum, be seen/sensed by an electronic eye like a photosensor/photodetector, not human eye, if the beam is just in air? For ...
2
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1answer
70 views

Carrying light through bleached water: how does it work?

Disclaimer: first time on Physics stack-exchange, I hope I'll be asking the question as per policy of this site, please help me edit if my wording seems off topic. I've seen a project to light up ...
12
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1answer
148 views

Sun in front of horizon after sunset; mirage or reflection?

The day before yesterday, I observed sunset while flying over the eastern Mediterranean. After the sun set, it seemed to 'continue' in front of the horizon. I managed to snatch a picture (sorry for ...
2
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1answer
48 views

light falling on a completely reflecting friction less mirror

If you had a perfectly reflective mirror whose face was perpendicular to the ground and was kept on a friction less track on the ground, and you shined a flashlight on it, what would happen? Would ...
11
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4answers
373 views

Effect of gravity upon light and bagels

According to this question and this web site, photons undergo twice the deflection from gravitational fields as do physical objects. However, the weak equivalence principle states that locally, ...
0
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1answer
48 views

Can someone reconcile the Boltzmann transport equation with the Maxwell equations for photons/light?

Having taking courses in both physics and nuclear engineering, I've noticed that the two fields tend to describe photons/light in two different settings. In nuclear engineering, the radiative ...
14
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3answers
920 views

Why is the bottom part of a candle flame blue?

What’s the explanation behind the bottom part of a candle flame being blue? I googled hard in vain. I read this. I don’t understand how it’s explained by the emission of excited molecular radicals in ...
0
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0answers
27 views

The path that light travels [duplicate]

This is a question that has puzzled me for some time. As a star emits light, the light travels away from the star. If you were to pick any spot on the star and draw a line extending outwards and then ...
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1answer
103 views

Experiments to the question : why wet is dark?

How can we prove the explanations for: why clothes get dark when they are wet, by experiments?
0
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1answer
46 views

How to transform infrared beam into visible range?

I am looking for an easy method of turning an infrared beam into a visible beam. There are some well-known ways to do it, for example a camera objective, but it that is very big and uncomfortable to ...
4
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2answers
106 views

Is there something equivalent to a diode for light?

In electronics a diode is a component allowing current passing in only one direction, and blocking the other side. I'm wondering if something similar exists for visible light or other EM waves, like ...
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2answers
462 views

Is there anything that could attract and trap a photon?

Is there any particle or anything that could attract and trap light or photon particle? Can anti photon particle attract photons and trap them ?
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2answers
83 views

Understanding colored shadows [closed]

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 ...
3
votes
2answers
119 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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2answers
132 views

How does light actually behave?

Senario: I am walking 5 meters/second and have a laser pointer that I shoot a burst of light from perpendicular to to the path I am walking on. Would the light travel perpendicular to the path from ...
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1answer
38 views

How does gas pressure increase the lifespan of Halogen tungsten lamps in the Halogen Cycle?

I am curious about this passage "Since quartz is very strong, the gas pressure can be higher,[5] which reduces the rate of evaporation of the filament, permitting it to run a higher temperature (and ...
35
votes
8answers
5k views

Will we ever be able to view the past?

By analogy with the sun, whose light is apparently reaching us in 8 minutes, it means that we are only viewing the sun 8 minutes ago when we look up at it. However, what if we were eventually able to ...
0
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0answers
60 views

Why do different wavelengths travel at different speeds through a medium? [duplicate]

Someone gave an explanation in another question: "Maxwell's equations predict that in a linear medium with permittivity ϵ and permeability μ, the speed of light in the medium will be v=1/ϵμ. When ...
4
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3answers
195 views

How to arrange mirrors so I can't see myself?

If I wanted to surround myself with mirrors how would I need to arrange them so that if I stood in the middle of them I couldn't see myself in any reflection? For simplicity let's just say we only ...
0
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1answer
126 views

Infrared Vs Visible Light

Infrared waves are widely used for quick heating objects, but a quick look at electromagnetic spectrum astonished me and raised a question that how come an infrared wave with lower energy compared to ...
55
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2answers
10k views

Why don't fluorescent lights produce shadows?

I have watched light sources such as incandescent lamps and other lamp sources; they have always made shadows. But a fluorescent lamp doesn't make any shadow. What is the reason behind the ...
1
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1answer
112 views

At what rate does light 'bend' around the surface of the earth?

Since the g force of earth is 9.8 m/s*2 does that mean light 'drops' at that rate as it travels past earth? Or is general relativity a lot more complex than that?
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3answers
107 views

What is the physical significance of the negative amplitude of a light wave?

I want to understand what is the physical significance of negative amplitude of a light wave? In an ac electrical circuit, I understand that negative amplitude signifies the amplitude measured when ...
1
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1answer
32 views

How long will a light bulb work isf the glass shell removed?

How long will a light bulb work if it gets its glass shell removed?
7
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2answers
951 views

How do we know the wavelength of colours?

Every site and video I have been on doesn't address it directly.specifically I want to know what is are the experiments we derive these wavelengths from and how do we calculate the wavelengths inspite ...